Electronic watermark embedding method, device, and program, and electronic watermark detecting method, device, and program

ABSTRACT

A digital watermark embedding apparatus for embedding embedding information into an input signal having dimensions equal to or greater than N(N is an integer equal to or greater than 2). The apparatus generates an embedding sequence based on the embedding information, generates an N−1-dimensional pattern based on the embedding sequence, generates an N-dimensional embedding pattern by modulating a periodic signal according to a value on the N−1-dimensional pattern, and superimposes the embedding pattern in the input signal and outputs it. A digital watermark detection apparatus measures a component of a predetermined periodic signal in a direction of a dimension of the input signal to obtain an N−1-dimensional pattern, obtains a detection sequence from values of the N−1 dimensional pattern, and detects the embedded digital watermark based on a size of correlation value between the detection sequence and an embedding sequence.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No. 12/282,062filed Sep. 8, 2008, which is a National Stage of PCT/JP07/053953, filedMar. 1, 2007, and claims the benefit of priority under 35 U.S.C. §119from Japanese Patent Application No. 2006-061745 filed Mar. 7, 2006, theentire contents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a digital watermark embedding method,apparatus and program, and a digital watermark detection method,apparatus and program. More particularly, the present invention relatesto a digital watermark embedding method, apparatus and program, and adigital watermark detection method, apparatus and program for embeddingseparate sub-information into an input signal such as a video signalsuch that it is imperceptible, and for reading the sub-information froma signal into which the sub-information is embedded.

BACKGROUND ART

As a conventional technique, there is a technique for protectingcopyright of digital content by embedding digital watermark into thedigital content. In addition, there is a technique to refer to meta datasuch as copyright information on digital content. Further, there is atechnique for taking a photograph of digital content, using a digitalcamera, via analog medium such as a printed matter as an advertisementso as to obtain information related to the advertisement by readingdigital watermark.

As a method for embedding digital watermark into a still image, adigital watermarking scheme of spectrum spreading type is disclosed, thescheme being for embedding an embedding sequence that is generated usinga pseudo-random number into a real part and an imaginary part of anorthogonal transformation region (Fourier transform region, for example)of the image, and performing detection using correlation between theembedding sequence and a detection sequence (refer to patent document 1,for example).

Also as to a video signal, generally, since the video signal is recordedas a sequence of frame images each being a still image, embedding ofdigital watermark becomes available by applying the digital watermarkscheme for the still image. For example, digital watermark for the videosignal can be realized by embedding digital watermark common to eachframe image of the video signal by using the digital watermark methoddescribed in the patent document 1.

When the still image in which digital watermark is embedded is illegallyused, it can be considered that a part of an image is cropped and it isused. In the case of the part of the image that is cropped, it cannot beascertained which part of the original image corresponds to the croppedpart in digital watermark detection that does not use the originalimage. This means that the embedded digital watermark pattern appears tobe translated by an arbitrary amount. That is, this means a state inwhich the digital watermark pattern is desynchronized in a spacedirection. This is called “spatial synchronization of digitalwatermark”, and it is necessary to maintain spatial synchronizationusing a method for clarifying the translation amount and the like fordetecting the digital watermark (generally, although spatialsynchronization of digital watermark may include correction ofgeometrical deformation such as affine transformation, the presentinvention is targeted for correction of translation).

Generally, the video signal is treated as a set of a plurality of stillimages (frames) continuing in a time direction. In a digital watermarkscheme for moving images, it is desired to be able to detect digitalwatermark from a set of a part of continuing frames in the set of theframes. For example, even when only one scene is cut away fromdistributed video content and it is used invalidly, by being able todetect digital watermark only from the invalidly used scene, effect ofinvalid use suppression can be expected. In addition, for example, inthe case when detecting digital watermark from a re-taken video that isobtained by taking video content being projected in a movie theaterusing a video camera, a start point of the video when embedding digitalwatermark and a start point of the re-taken video are shiftedinevitably. It is desired to be able to detect digital watermark also insuch a case. In addition, for example, an application can be consideredfor detecting digital watermark from a video that is obtained by takinga scene currently being displayed in video content using a camera of aportable terminal and the like so as to obtain related information. Inthese examples, since it cannot be ascertained beforehand which part inthe video in which digital watermark is embedded is cut away, it isnecessary, when performing digital watermark detection, to know asubject part for detection corresponds to which position in the signalembedded as digital watermark. This is called temporal synchronizationof digital watermark.

The spatial synchronization and the temporal synchronization in theconventional digital watermark scheme are broadly classified as follows.

(1) Exhaustive search: exhaustively trying detection of digitalwatermark successively for each of all amounts of desynchronization thatcan be considered;

(2) Embedding a signal for synchronization: embedding a signal forsynchronization separately from digital watermark and detecting it forsynchronization.

For example, in the digital watermarking method described in the patentdocument 1, a signal for detecting a spatial translation amount ofdigital watermark is embedded together with embedding information, andexhaustive search for amounts of desynchronization of the signal isefficiently performed using discrete Fourier transform so as to performspatial synchronization.

-   -   [Patent document 1] Japanese Laid Open Patent Application        2003-219148

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, there are following problems in the conventional digitalwatermark embedding method for video.

Problem of robustness to high compression and re-taking:

For example, there is a case in which detection becomes difficult whenapplying (high compression) moving image irreversible coding of highcompression ratio such as MPEG1/2/4, WMV (Windows (registered trademark)Media Video), DiVX and H.264/AVC, or when taking (re-taking), again, avideo output on a display device such as a screen and a display using avideo camera or a camera mounted in a cellular phone or the like.

In addition, it becomes necessary to embed digital watermark strongly inorder to be able to perform detection even when the high compression orre-taking is performed, so that image quality of the video is lowered asa result.

Contrary, for giving adequate robustness to the high compression and there-taking and the like while maintaining adequate image quality, it isnecessary to shorten the information length embedded in the video.

Problem of Spread Sequence Length:

In a document, Susumu Yamamoto, Takao Nakamura, Youichi Takashima,Atsushi Katayama, Ryo Kitahara, Takashi Miyatake, “Consideration onevaluation of detectability for frame-based video watermarking”, Forumon information technology, FIT2005, J-029, 2005, it is described that,in a digital watermark scheme using spectrum spreading and correlationcalculation, reliability of detection of digital watermark increases byincreasing the spread sequence length of spectrum spreading. In thedigital watermark scheme in the before-mentioned patent document 1, thenumber of frequency coefficient positions in the orthogonaltransformation region in which the embedding sequence can be embedded islimited due to restriction of symmetry of Fourier coefficient forobtaining real values by reverse transform. That is, due to restrictionthat Fourier coefficients in symmetric positions are conjugate complexnumbers, the frequency coefficients to which an embedding sequence canbe embedded are substantially limited to half the whole frequencycoefficients, so that it was difficult to increase the spread sequencelength in the spectrum spreading.

Problem of Synchronization

In addition, in the conventional methods for spatial synchronization andtemporal synchronization in digital watermarking, there are followingproblems.

First, as to the method by exhaustive search, since it takes much timeto search all of the desynchronization amounts, it is not realistic.

In addition, in the method embedding the signal for synchronization,modification amount for the signal is increased by the signal for thesynchronization, so that the quality of the signal is decreased as awhole. For example, as for a video, it leads to deteriorating thequality of the video. In addition, the signal for synchronization itselfcontributes as a noise component against detection of embeddinginformation, so that there is a possibility that detection capabilitydeteriorates. In addition, a distinctive signal for synchronization canbe easily predicted, and there is a possibility that the signal itselfbecomes a subject of attack so that security is deteriorated.

Especially, there is a following problem in temporal synchronization fora video.

When a video displayed on a screen or a TV is taken by a video camera ora camera of a cellular phone or the like, re-sampling occurs insub-frames since a frame rate of reproduction and a frame rate for videotaking are not synchronized with each other, so that synchronization isfurther difficult. In addition, when using a processor of lowperformance such as the cellular phone, there is a case in which theframe rate for video taking is not stable so that timing of sampling isslightly shifted, and it is also a factor for making the synchronizationdifficult.

The present invention is contrive in view of the above-mentioned points,and an object is to provide a digital watermark embedding technique anda digital watermark detection technique in which robustness is high forhigh compression and re-taking, the spread sequence length can beincreased, and temporal synchronization/space synchronization becomeunnecessary or temporal synchronization/space synchronization can beachieved easily.

Means for Solving the Problem

The present invention can be configured as a digital watermark embeddingmethod for embedding embedding information, as digital watermark, intoan input signal having dimensions equal to or greater than N(N is aninteger equal to or greater than 2) such that it is imperceptible tohuman senses in a digital watermark embedding apparatus includingembedding sequence generation means, array generation means, modulationmeans, storage means, and embedding pattern superimposing means,wherein, the embedding sequence generation means generates an embeddingsequence based on the embedding information to store it in first storagemeans;

the array generation means generates a N−1-dimensional pattern based onthe embedding sequence in the first storage means;

the modulation means modulates the periodic signal according to a valueon the N−1-dimensional pattern to generate a N-dimensional embeddingpattern and store it in a second storage means; and the embeddingpattern superimposing means obtains the N-dimensional embedding patternstored in the second storage means to superimpose the embedding patternon the input signal so as to embed it.

The present invention can be also configured as a digital watermarkembedding method for embedding embedding information, as digitalwatermark, into an input signal having dimensions equal to or greaterthan N(N is an integer equal to or greater than 2) such that it isimperceptible to human senses in a digital watermark embedding apparatusincluding embedding sequence generation means, array generation means,transform means, storage means, embedding pattern superimposing means,and inverse transform means, wherein,

the embedding sequence generation means generates an embedding sequencebased on the embedding information to store it in first storage means;

the array generation means generates a N−1-dimensional pattern based onthe embedding sequence stored in the first storage means to stored it insecond storage means;

the transform means orthogonal transforms the input signal to obtain atransformed signal;

the embedding pattern superimposing means superimposes theN−1-dimensional pattern stored in the second storage means on a N−1dimensional plane that is a part of the transformed signal to obtainbefore-inverse transform signal; and

the inverse transform means orthogonal inverse transforms the beforeinverse transform signal to obtain an embedded signal.

The present invention can be also configured as a digital watermarkdetecting method for detecting digital watermark that is embeddedbeforehand into an input signal having dimensions equal to or greaterthan N(N is an integer equal to or greater than 2) such that it isimperceptible to human senses in a digital watermark detection apparatusincluding demodulation means, detection sequence extraction means,correlation value calculation means, and storage means, wherein, thedemodulation means measures a component of a predetermined periodicsignal in a direction of a dimension in the input signal to obtain aN−1-dimensional pattern;

the detection sequence extraction means obtains a detection sequencefrom values of the N−1-dimensional pattern to store the detectionsequence in storage means; and

the correlation value calculation means detects the embedded digitalwatermark based on a size of a correlation value between the detectionsequence stored in the storage means and an embedding sequence.

In addition, the present invention can be also configured as anapparatus applicable for carrying out each of the above-mentionedmethods, and as a program for causing a computer to execute the processprocedures of each of the above-mentioned methods.

Effect of the Invention

According to the present invention, a technique for embeddinginformation having long information length as digital watermark in whichthere is sufficient robustness and quality deterioration is suppressedcan be realized even when large modification is applied to a digitalwatermark embedded signal like a video signal to which moving imageirreversible coding of high compression is applied or which is re-takenfrom a video output on a display device. In addition, a technique forperforming digital watermark detection in which synchronization is notnecessary or synchronization can be performed easily and at high speedcan be realized. That is, according to the present invention, fastdigital watermark embedding/detection in which increase of process timedue to synchronization processing and signal deterioration due tosynchronization signal embedding are prevented, robustness and detectionperformance are high, and quality deterioration is small becomepossible.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a flowchart showing an outline of a digital watermarkembedding method in an embodiment of the present invention;

FIG. 1B is a flowchart showing an outline of a digital watermarkdetection method in an embodiment of the present invention;

FIG. 2 is a diagram showing a schematic configuration of a digitalwatermark embedding apparatus and a digital watermark detectionapparatus in an embodiment of the present invention;

FIG. 3 is an example of an embedding signal after modulation when N=2;

FIG. 4A is a configuration example 1 of a periodic signal;

FIG. 4B is a configuration example 2 of a periodic signal;

FIG. 4C is a configuration example 3 of a periodic signal;

FIG. 5A is an example 1 of autocorrelation function of a periodicsignal;

FIG. 5B is an example 2 of autocorrelation function of a periodicsignal;

FIG. 5C is an example 3 of autocorrelation function of a periodicsignal;

FIG. 6A is a locus 1 of a function h0 corresponding to a periodic signalon a complex plane;

FIG. 6B is a locus 2 of a function h0 corresponding to a periodic signalon a complex plane;

FIG. 6C is a locus 3 of a function h0 corresponding to a periodic signalon a complex plane;

FIG. 7A is an example 1 of two periodic signals that are orthogonal;

FIG. 7B is an example 2 of two periodic signals that are orthogonal;

FIG. 8A is an example 1 of a signal after being desynchronized;

FIG. 8B is an example 2 of a signal after being desynchronized;

FIG. 9 is an example of a locus of Q(x) by desynchronization;

FIG. 10 shows configuration examples of a digital watermark embeddingapparatus and a digital watermark detection apparatus according to afirst embodiment of the present invention;

FIG. 11 is a flowchart showing operation of the digital watermarkembedding apparatus according to a first embodiment of the presentinvention;

FIG. 12 is a configuration example of a complex pattern generation unitaccording to a first embodiment of the present invention;

FIG. 13 is a flowchart showing processes of the complex patterngeneration unit of the first embodiment of the present invention;

FIG. 14 is a flowchart of detailed operation of an embedding sequencegeneration unit in the first embodiment of the present invention;

FIG. 15 is a configuration example of symbols in the first embodiment ofthe present invention;

FIG. 16 is a flowchart of operation of a complex array generation unitin the first embodiment of the present invention;

FIG. 17 is a configuration example of a complex array in the firstembodiment of the present invention;

FIG. 18 is a configuration example of a temporal modulation unit in thefirst embodiment of the present invention;

FIG. 19 is a flowchart of operation of the temporal modulation unit inthe first embodiment of the present invention;

FIG. 20 is an example for repeatedly embedding an embedding pattern in atime direction in the first embodiment of the present invention;

FIG. 21 is an example for superimposing an embedding pattern by tilingit vertically and horizontally in the first embodiment of the presentinvention;

FIG. 22 is an example for superimposing an embedding pattern byenlarging it in the first embodiment of the present invention;

FIG. 23 is a flowchart of operation of a digital watermark detectionapparatus in the first embodiment of the present invention;

FIG. 24 is an example for calculating a characteristic amount of anembedded signal to extract it in the first embodiment of the presentinvention;

FIG. 25 shows a configuration example of a temporal demodulation unit inthe first embodiment of the present invention;

FIG. 26 is a flowchart of operation of the temporal demodulation unit inthe first embodiment of the present invention;

FIG. 27 is a configuration example using difference/differentiation ofthe temporal demodulation unit in the first embodiment of the presentinvention;

FIG. 28 is a configuration example of a detection information extractionunit in the first embodiment of the present invention;

FIG. 29 is a flowchart of operation of the detection informationextraction unit in the first embodiment of the present invention;

FIG. 30 is a flowchart of detailed operation of the detection sequenceextraction unit in the first embodiment of the present invention;

FIG. 31 is a configuration example of a temporal modulation unit in asecond embodiment of the present invention;

FIG. 32 is a flowchart showing operation of the temporal modulation unitin the second embodiment of the present invention;

FIG. 33 is a configuration example of the temporal demodulation unit inthe second embodiment of the present invention;

FIG. 34 is a flowchart of operation of a temporal demodulation unit inthe second embodiment of the present invention;

FIG. 35 is a configuration example using difference/differentiation inthe second embodiment of the present invention;

FIG. 36 is a configuration example of a complex pattern generation unitin a third embodiment of the present invention;

FIG. 37 is a flowchart of operation of the complex pattern generationunit in the third embodiment of the present invention;

FIG. 38A is an example 1 of an element range of the complex array in thecomplex array generation unit in the third embodiment of the presentinvention;

FIG. 38B is an example 2 of the element range of the complex array;

FIG. 38C is an example 3 of the element range of the complex array;

FIG. 38D is an example 4 of the element range of the complex array;

FIG. 38E is an example 5 of the element range of the complex array;

FIG. 38F is an example 6 of the element range of the complex array;

FIG. 39A is an example 7 of the element range of the complex array;

FIG. 39B is an example 8 of the element range of the complex array;

FIG. 39C is an example 9 of the element range of the complex array;

FIG. 39D is an example 10 of the element range of the complex array;

FIG. 39E is an example 11 of the element range of the complex array;

FIG. 39F is an example 12 of the element range of the complex array;

FIG. 40 is a configuration example of a detection information extractionunit in the third embodiment of the present invention;

FIG. 41 is a flowchart of operation of the detection informationextraction unit in the third embodiment of the present invention;

FIG. 42 is a configuration of a detection information extraction unit ina fourth embodiment of the present invention;

FIG. 43 is a flowchart of the operation of the detection informationextraction unit in the fourth embodiment of the present invention;

FIG. 44 is a diagram for explaining an example of a method for detectinga bit value in the fourth embodiment of the present invention;

FIG. 45 is a configuration example of a digital watermark detectionapparatus in a fifth embodiment of the present invention;

FIG. 46 is a flowchart showing operation of the digital watermarkdetection apparatus in the fifth embodiment of the present invention;

FIG. 47 is a configuration example of a synchronization detection unitin the fifth embodiment of the present invention;

FIG. 48 is a flowchart of operation of the synchronization detectionunit in the fifth embodiment of the present invention;

FIG. 49 is a configuration example of the detection informationextraction unit in the fifth embodiment of the present invention;

FIG. 50 is another configuration example of the detection informationextraction unit in the fifth embodiment of the present invention;

FIG. 51 is a configuration example of a temporal modulation unit in asixth embodiment of the present invention;

FIG. 52 is a configuration example of a digital watermark embeddingapparatus and a digital watermark detection apparatus of the seventhembodiment of the present invention;

FIG. 53 is a flowchart of operation of the digital water is a flowchartof operation of the digital watermark embedding apparatus in a seventhembodiment of the present invention;

FIG. 54 is a configuration example of a complex pattern generation unitin the seventh embodiment of the present invention;

FIG. 55 is a flowchart of operation of the complex pattern generationunit in the seventh embodiment of the present invention;

FIG. 56 is a flowchart of operation of the digital watermark detectionapparatus in the seventh embodiment of the present invention;

FIG. 57 is a configuration example of the detection informationextraction unit in the seventh embodiment of the present invention;

FIG. 58 is an example for connecting synchronization displacementamounts in the seventh embodiment of the present invention;

FIG. 59 is a flowchart of operation of the digital watermark embeddingapparatus in the eighth embodiment of the present invention;

FIG. 60 is a configuration example of the complex pattern generationunit in the eighth embodiment of the present invention;

FIG. 61 is a flowchart of operation of the complex pattern generationunit in the eighth embodiment of the present invention;

FIG. 62 is an example for embedding a plurality of pieces of informationcontinuously in a time division manner in the eighth embodiment of thepresent invention;

FIG. 63 is a configuration example of the digital watermark detectionapparatus in the eighth embodiment of the present invention;

FIG. 64 is a flowchart of operation of the digital watermark detectionapparatus in the eighth embodiment of the present invention;

FIG. 65 is an example for detecting a synchronization pattern from adesynchronized position in the eighth embodiment of the presentinvention;

FIG. 66 is a configuration example of the detection informationextraction unit in the eighth embodiment of the present invention;

FIG. 67 is a flowchart of operation of the detection informationextraction unit in the eighth embodiment of the present invention;

FIG. 68 shows a configuration example of a digital watermark embeddingapparatus and a digital watermark detection apparatus in a ninthembodiment of the present invention; and

FIG. 69 is a flowchart of operation of the digital watermark embeddingapparatus in the ninth embodiment of the present invention.

DESCRIPTION OF REFERENCE SIGNS

-   102 first storage means-   103 second storage means-   100 digital watermark embedding apparatus-   110 complex pattern generation unit-   111 embedding sequence generation means, embedding sequence    generation unit-   112 array generation means, array generation unit-   113 N−1-dimensional inverse Fourier transform unit-   114 embedding information dividing unit-   115 synchronization sequence generation unit-   116 complex array generation unit-   117 embedding sequence generation unit-   120 array generation unit-   130 modulation means, temporal modulation unit-   131 frequency signal generation unit-   132 modulation unit-   133 adding unit-   134 one-dimensional inverse Fourier transform unit-   136 modulation unit-   140 embedding pattern superimposing means, embedding pattern    superimposing unit-   150 first storage unit-   160 second storage unit-   200 digital watermark detection apparatus-   202 storage means-   210 demodulation means, temporal demodulation unit-   211 periodic signal generation unit-   212 demodulation unit-   213 complex pattern configuration unit-   214 one-dimensional Fourier transform unit-   215 signal differentiation unit-   216 one-dimensional Fourier transform unit-   220 detection information extraction unit-   221 detection sequence extraction means, detection sequence    extraction unit-   222 correlation value calculation means, correlation value    calculation unit-   223 maximum value determination unit-   224 detection information reconfiguration unit-   225 N−1-dimensional Fourier transform unit-   226 complex correlation value calculation unit-   227 absolute value calculation unit-   250 pattern storage unit-   300 digital watermark detection apparatus-   310 temporal demodulation unit-   320 synchronization detection unit-   321 complex detection sequence extraction unit-   322 complex correlation value calculation unit-   323 absolute value calculation unit-   324 synchronization detection maximum value determination unit-   325 phase calculation unit-   330 detection information extraction unit-   331 detection sequence extraction unit-   332 correlation value calculation unit-   333 maximum value determination unit-   334 detection information reconfiguration unit-   500 digital watermark embedding apparatus-   510 complex pattern generation unit-   511 embedding sequence generation unit-   512 complex array generation unit-   520 temporal modulation unit-   530 embedding pattern superimposing unit-   600 digital watermark detection apparatus-   610 temporal demodulation unit-   620 synchronization detection unit-   630 detection information extraction unit-   631 detection sequence extraction unit-   632 correlation value calculation unit-   633 maximum value determination unit-   634 detection information reconfiguration unit-   700 digital watermark detection apparatus-   710 embedded signal dividing unit-   720 synchronization temporal demodulation unit-   730 synchronization detection unit-   740 synchronized signal dividing unit-   750 temporal demodulation unit-   760 detection information extraction unit-   761 detection sequence extraction unit-   762 correlation value calculation unit-   763 maximum value determination unit-   764 detection information re-configuration unit-   765 detection information connecting unit-   800 digital watermark embedding apparatus-   810 complex pattern generation unit-   820 embedding pattern superimposing unit-   830 before-embedding signal transform unit-   840 embedded signal inverse transform unit-   850 first storage unit-   904 intermediate complex pattern-   911 embedding information-   912 before-embedding signal-   913 embedding sequence-   914 detection information-   917 synchronization sequence-   921 embedding complex pattern-   923 embedded signal-   961 detection complex pattern-   1113 detection sequence-   1114 correlation value-   1115 detection complex array-   1116 complex correlation value-   1117 absolute value-   1118 detection complex number sequence-   1501 detection complex pattern-   1502 synchronization displacement amount-   1511 detection complex sequence-   1512 complex correlation value-   1513 absolute value-   1521 detection sequence-   1522 correlation value-   3111 embedding information-   3112 before-embedding signal-   3113 embedded signal-   3114 detection information-   3121 embedding complex pattern-   3122 embedding pattern-   3161 detection complex pattern-   3162 synchronization displacement amount-   3213 embedding sequence-   3313 detection sequence-   3314 correlation value-   3613 detection sequence-   3314 correlation value-   3613 detection sequence-   3614 correlation value-   3615 partial detection information-   3812 detection information-   3813 synchronization complex pattern-   3814 synchronization displacement amount-   3815 detection complex pattern-   3816 partial embedded signal-   3817 synchronized partial signal-   4021 embedding complex pattern-   4022 transformed before-embedding signal-   4023 before inverse transform embedded signal

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

First, an outline of embodiments of the present invention is described.FIG. 1A is a flowchart showing an outline of a digital watermarkembedding method in an embodiment of the present invention.

The digital watermark embedding method is a digital watermark embeddingmethod for embedding embedding information, as digital watermark, intoan input signal having dimensions equal to or greater than N(N is aninteger equal to or greater than 2) such that it is imperceptible tohuman senses in a digital watermark embedding apparatus includingembedding sequence generation means, array generation means, modulationmeans, storage means, and embedding pattern superimposing means. Thismethod includes: an embedding sequence generation step (step 1) in whichthe embedding sequence generation means generates an embedding sequencebased on the embedding information to store it in first storage means,an array generation step (step 2) in which the array generation meansgenerates a N−1-dimensional pattern based on the embedding sequence inthe first storage means, a modulation step (step 3) in which themodulation means modulates a periodic signal according to a value on theN−1-dimensional pattern to generate a N-dimensional embedding patternand store it in a second storage means, and an embedding patternsuperimposing step (step 4) in which the embedding pattern superimposingmeans obtains the N-dimensional embedding pattern stored in the secondstorage means to superimpose the embedding pattern on the input signalso as to embed it.

FIG. 1B is a flowchart showing an outline of a digital watermarkdetection method in an embodiment of the present invention. The digitalwatermark detection method is a digital watermark detection method fordetecting digital watermark that is embedded into an input signal havingdimensions equal to or greater than N such that it is imperceptible tohuman senses in a digital watermark detection apparatus includingdemodulation means, detection sequence extraction means, correlationvalue calculation means, and storage means.

This method includes: a demodulation step (step 11) in which thedemodulation means measures a component of a predetermined periodicsignal in a direction of a dimension in the input signal to obtain aN−1-dimensional pattern, a detection sequence extraction step (step 12)in which the detection sequence extraction means obtains a detectionsequence from values of the N−1-dimensional pattern to store thedetection sequence in storage means, and a correlation value calculationstep (step 13) in which the correlation value calculation means detectsthe embedded digital watermark based on a size of a correlation valuebetween the detection sequence stored in the storage means and anembedding sequence.

FIG. 2 is a diagram showing schematic configurations of a digitalwatermark embedding apparatus and a digital watermark detectionapparatus in an embodiment of the present invention.

The digital watermark embedding apparatus of the present embodiment is adigital watermark embedding apparatus 100 for embedding embeddinginformation, as digital watermark, into an input signal havingdimensions equal to or greater than N (N is an integer equal to orgreater than 2) such that it is imperceptible to human senses,including: embedding sequence generation means 111 configured togenerate an embedding sequence based on the embedding information tostore it in first storage means 102; array generation means 112configured to generate a N−1-dimensional pattern based on the embeddingsequence in the first storage means 102; modulation means 130 configuredto modulate a periodic signal according to a value on theN−1-dimensional pattern to generate a N-dimensional embedding patternand store it in second storage means 103; and embedding patternsuperimposing means 140 configured to obtain the N-dimensional embeddingpattern stored in the second storage means 103 to superimpose theembedding pattern on the input signal so as to embed it.

The digital watermark detection apparatus of the present embodiment is adigital watermark detection apparatus 200 for detecting digitalwatermark that is embedded into an input signal having dimensions equalto or greater than N such that it is imperceptible to human senses,including: demodulation means 210 configured to measure a component of apredetermined periodic signal in a direction of a dimension in the inputsignal to obtain a N−1-dimensional pattern; detection sequenceextraction means 221 configured to obtain a detection sequence fromvalues of the N−1-dimensional pattern to store the detection sequence instorage means 202; and correlation value calculation means 222configured to detect the embedded digital watermark based on a size of acorrelation value between the detection sequence stored in the storagemeans 250 and an embedding sequence.

In the following, embodiments of the present invention are described indetail with reference to figures.

In the following, first, basic concept that is a principle of thepresent invention and the examples are described, and after that,concrete embodiments of the digital watermark embedding apparatus, thedigital watermark detection apparatus and the methods are described.

[Basic Concept]

First, a basic concept that is a principle of the present embodiment isshown in the following.

(1) Digital Watermarking Model Based on Complex Correlation:

In the following, correlation using type digital watermarking that usesa complex number sequence is shown.

By the way, it is needless to say that a part using a complex number inthe present specification in the following can be replaced with atwo-dimensional vector as a same concept.

Embedding) A signal sequence i that is a subject for embedding and adigital watermark sequence w are defined as follows.i={i₁, i₂, . . . , i_(L)}εC^(L)  (1)w={w₁, w₂, . . . , w_(L)}εC^(L)  (2)In the definitions, C is a set of the whole complex numbers, and w is apseudo-random number sequence of an average 0.

An embedded signal sequence i′ is obtained by embedding w into i.i′=i+w  (3)

Detection) Considering i″ in which the phase of i′ is shifted by Δθ dueto desynchronization,i″=i′e^(jΔθ)  (4)wherein j is the imaginary unit.

A correlation value between i″ and w is calculated using the followingequation to detect digital watermark,ρ=i″·w*  (5)wherein “w*” is a number sequence including conjugate complex numbers ofeach element of w, “·” indicates inner product calculation in which thesequence is regarded as a vector. By the way, such correlationcalculation between complex number sequences is called complexcorrelation.

$\begin{matrix}\begin{matrix}{\rho = {i^{''} \cdot w^{*}}} \\{= {\left( {i + w} \right){{\mathbb{e}}^{j\;\Delta\;\theta} \cdot w^{*}}}} \\{= {{\mathbb{e}}^{j\;\Delta\;\theta}\left( {{i \cdot w^{*}} + {w \cdot w^{*}}} \right)}} \\{= {{\mathbb{e}}^{j\;\Delta\;\theta}\left( {{\sum\limits_{k = 1}^{L}{i_{k}w_{k}^{*}}} + {\sum\limits_{k = 1}^{L}{w_{k}w_{k}^{*}}}} \right)}} \\{= {{\mathbb{e}}^{j\;\Delta\;\theta}\left( {{\sum\limits_{k = 1}^{L}{i_{k\;}w_{k}^{*}}} + {\sum\limits_{k = 1}^{L}{w_{k}}^{2}}} \right)}}\end{matrix} & (6)\end{matrix}$In the equation, “w*_(k)” indicates a conjugate complex number of w_(k).

When i and w are independent and when L is sufficiently large, anexpected value of Σi_(k)w*_(k) is 0, and

$\begin{matrix}{\rho \sim {\left( {\sum\limits_{k = 1}^{L}{w_{k}}^{2}} \right){\mathbb{e}}^{j\;\Delta\;\theta}}} & (7)\end{matrix}$therefore,

-   -   Detection becomes available irrespective of the phase shift        amount Δθ by obtaining an embedding value by which an absolute        value of ρ becomes maximum. That is, detection becomes possible        without synchronization.    -   The phase shift amount Δθ can be calculated by obtaining the        argument of ρ.

Following two selection methods can be considered for w_(k).

1) For example, a case in which it is selected only from real numberssuch as selecting a value from among {+1, −1}.

2) For example, a case in which it is selected such that it isdistributed over the complex number space such as selecting a value fromamong following complex numbers.{±√{square root over (1/2)}±j√{square root over (1/2)}}

In the case of 1), the phases of watermark pattern components w on theembedded signal sequence i′ are aligned. In the case of 2), the phasesare dispersed. In either case, the expected value of Σi_(k)w*_(k)becomes 0 so that detection of digital watermark becomes possible. But,under a condition in which dispersion of |w_(k)| is equalized to alignenergy of the digital watermark components, when 1) and 2) are compared,dispersion of |Σi_(k)w*_(k)| in 2) becomes smaller. This means thateffect of noise component provided by the signal sequence i of theembedding subject to the value of ρ becomes small, so that detection ofhigher reliability becomes possible.

(2) Temporal Synchronization Unnecessary Digital Watermarking byTemporal Direction Single Frequency Embedding:

As an example of digital watermarking in which the phase is shifted byΔθ due to desynchronization, an example for performing embedding to asingle frequency in temporal direction is shown.

More particularly, for example, an example for modulating a complexnumber pattern that is configured in the spatial direction of the videoand embedding it into a single frequency in a temporal direction isshown.

Embedding) N−1-dimensional complex pattern P(x) is embedded into aN-dimensional signal sequence, wherein x is a vector representing aposition in a N−1-dimensional space as follows.x═(x₁, x₂, . . . , x_(N−1))  (8)

N-th dimension is regarded as a time axis, and a periodic complexfunction f(t) is prepared. For example,

$\begin{matrix}\begin{matrix}{{f(t)} = {\mathbb{e}}^{j\;\omega\; t}} \\{{\cos\;\omega\; t} + {j\;\sin\;\omega\; t}}\end{matrix} & (9)\end{matrix}$wherein j is the imaginary unit, ω is angular velocity representing theperiod of f(t).

N-dimensional real number signal W(x, t) is obtained in which the realpart and the imaginary part of P(x) are AM modulated and combined by thereal part and the imaginary part of f(t) respectively as follows,

$\begin{matrix}\begin{matrix}{{W\left( {x,t} \right)} = {{{\left\lbrack {P(x)} \right\rbrack}\cos\;\omega\; t} + {{{??}\left\lbrack {P(x)} \right\rbrack}\sin\;\omega\; t}}} \\{= {\left\lbrack {{P(x)} \times {f^{*}(t)}} \right\rbrack}} \\{= {\left\lfloor {{P(x)}{\mathbb{e}}^{{- j}\;\omega\; t}} \right\rfloor}}\end{matrix} & (10)\end{matrix}$wherein f*(t) is a complex function for obtaining a conjugate complexnumber of f(t).

FIG. 3 shows an example of W(x, t) when N=2. In the figure, the thicklines indicate the values of w(x, t) which is represented as a periodicsignal, in the t axis direction, in which the phase is shifted for eachposition x.

By such modulation, phase and amplitude of f(t) are modulated by anargument and an absolute value of the complex number value of P(x).

By embedding W(x, t) into an embedding subject signal I(x, t) to obtainan embedded signal I′ (x, t).I′(x, t)=I(x, t)+W(x, t)  (11)

Detection) Considering a signal I″(x, t) in which I′(x, t) is shifted byΔt due to desynchronization.

$\begin{matrix}\begin{matrix}{{I^{''}\left( {x,t} \right)} = {I^{\prime}\left( {x,{t + {\Delta\; t}}} \right)}} \\{= {{I\left( {x,{t + {\Delta\; t}}} \right)} + {W\left( {x,{t + {\Delta\; t}}} \right)}}} \\{= {{I\left( {x,{t + {\Delta\; t}}} \right)} + {\left\lbrack {{P(x)}{\mathbb{e}}^{{- j}\;{\omega{({t - {\Delta\; t}})}}}} \right\rbrack}}}\end{matrix} & (12)\end{matrix}$

For example, considering a video signal and the like, the amount ofdesynchronization in the temporal direction becomes constant normallyeven though positions in the space are different when re-taking by avideo camera or analog transformation is performed. (When temporaldirection desynchronization which is different in each spatial positionis added as an attack to digital watermark, since image quality isremarkably deteriorated so that the value as video content is damaged,the desynchronization cannot be done as an attack) Therefore, it can beconsidered that the amount Δt of desynchronization is constantirrespective of the position x as mentioned above.

In addition, for example, considering an image signal, when onlytranslation of the image is added, although the position x of thelateral direction of the image signal is different, the amount oftranslation applied in the longitudinal direction becomes constant. Alsoin this case, it can be considered that the amount Δt ofdesynchronization in the longitudinal direction (t direction) isconstant irrespective of the position x in the lateral direction.

Now, the following integration is calculated for demodulating I″(x, t),provided in a section 0≦t≦T (T is an integral multiple of the period off (t)), by f(t).

$\begin{matrix}\begin{matrix}{{Q(x)} = {\int_{0}^{T}{{I^{''}\left( {x,\tau} \right)}f^{*}\ {\mathbb{d}\tau}}}} \\{= {\int_{0}^{T}{{I^{''}\left( {x,\tau} \right)}{\mathbb{e}}^{{- j}\;\omega\;\tau}{\mathbb{d}\tau}}}} \\{= {{\int_{0}^{T}{{I\left( {x,{\tau + {\Delta\; t}}} \right)}{\mathbb{e}}^{{{- j}\;\omega\;\tau}\;}}} + {{\left\lbrack {{P(x)}{\mathbb{e}}^{{- j}\;{\omega{({\tau + {\Delta\; t}})}}}} \right\rbrack}{\mathbb{e}}^{{- j}\;\omega\;\tau}\ {\mathbb{d}\tau}}}} \\{= {{N\left( {x,{\Delta\; t}} \right)} + {\frac{T\;{\mathbb{e}}^{j\;\omega\;\Delta\; t}}{2}{P(x)}}}}\end{matrix} & (13)\end{matrix}$In the equation,N(x, Δt)=∫₀ ^(T) I(x, τ+Δt)e ^(−jωτ) dτand the following relationship is used.

$\begin{matrix}{{\int_{0}^{T}{{\left\lbrack {\left( {a + {j\; b}} \right){\mathbb{e}}^{{- j}\;{\omega{({\tau + {\Delta\; t}})}}}} \right\rbrack}{\mathbb{e}}^{{- j}\;\omega\; t}\ {\mathbb{d}\tau}}} = \,{{\int_{0}^{T}{\left( {{a\frac{{\mathbb{e}}^{- {{j\omega}{({\tau + {\Delta\; t}})}}} + {\mathbb{e}}^{j\;{\omega{({\tau + {\Delta\; t}})}}}}{2}} + {b\frac{{\mathbb{e}}^{- {{j\omega}{({\tau + {\Delta\; t}})}}} - {\mathbb{e}}^{{j\omega}{({\tau + {\Delta\; t}})}}}{2j}}} \right){\mathbb{e}}^{{- {j\omega}}\;\tau}{\mathbb{d}\tau}}} = {{\int_{0}^{T}{\left( {{a\frac{{\mathbb{e}}^{- {{j\omega}{({{2\tau} + {\Delta\; t}})}}} + {\mathbb{e}}^{j\;{\omega\Delta}\; t}}{2}} + {b\frac{{\mathbb{e}}^{{- j}\;{\omega{({{2\tau} + {\Delta\; t}})}}} - {\mathbb{e}}^{j\;{\omega\Delta}\; t}}{2j}}} \right){\mathbb{d}\tau}}} = {{{{\mathbb{e}}^{j\;{\omega\Delta}\; t}{\int_{0}^{T}\frac{a}{b}}} - {\frac{b}{2j}{\mathbb{d}\tau}}} = {\frac{T\;{\mathbb{e}}^{j\;\omega\;\Delta\;\tau}}{2}{\left( {a + {j\; b}} \right).}}}}}} & (14) \\{\mspace{79mu}{{Thus},}} & \; \\{\mspace{79mu}{{\int_{0}^{T}{{\left\lbrack {{P(x)}{\mathbb{e}}^{{- j}\;{\omega{({\tau + {\Delta\; t}})}}}} \right\rbrack}{\mathbb{e}}^{{- j}\;\omega\;\tau}\ {\mathbb{d}\tau}}} = {\frac{T\;{\mathbb{e}}^{j\;\omega\;\Delta\;\tau}}{2}{P(x)}}}} & (15)\end{matrix}$

By the way, in this example, although an example is described for a casein which the signal I″(x, t) is obtained as a continuous signal, alsowhen the signal I″(x, t) is obtained as a discrete signal, similarprocessing is available using product-sum operation instead ofintegration.

That is,

$\begin{matrix}{{{\sum\limits_{\tau = 0}^{T - 1}{{\left\lbrack {\left( {a + {j\; b}} \right){\mathbb{e}}^{{- j}\;{\omega{({\tau + {\Delta\; t}})}}}} \right\rbrack}{\mathbb{e}}^{{- j}\;{\omega\tau}}}} = {{{{\mathbb{e}}^{j\;\omega\;\Delta\; t}{\sum\limits_{\tau = 0}^{T - 1}\frac{a}{2}}} - \frac{b}{2j}} = {\frac{T\;{\mathbb{e}}^{j\;\omega\;\Delta\; t}}{2}\left( {a + {j\; b}} \right)}}}\mspace{79mu}{{thus},}} & (16) \\{\mspace{79mu}{{\sum\limits_{\tau = 0}^{T - 1}{{\left\lbrack {{P(x)}{\mathbb{e}}^{{- j}\;{\omega{({\tau + {\Delta\; t}})}}}} \right\rbrack}{\mathbb{e}}^{{- j}\;\omega\;\tau}}}\  = {\frac{T\;{\mathbb{e}}^{j\;\omega\;\Delta\;\tau}}{2}{P(x)}}}} & (17) \\{\mspace{79mu}{\begin{matrix}{{Q(x)} = {\sum\limits_{\tau = 0}^{T - 1}{{I^{''}\left( {x,\tau} \right)}{f^{*}\ (\tau)}}}} \\{= {\sum\limits_{\tau = 0}^{T - 1}{{I^{''}\left( {x,\tau} \right)}{\mathbb{e}}^{{- j}\;\omega\;\tau}}}} \\{{= {{\sum\limits_{\tau = 0}^{T - 1}{{I\left( {x,{\tau + {\Delta\; t}}} \right)}{\mathbb{e}}^{{{- j}\;\omega\;\tau}\;}}} + {{\left\lbrack {{P(x)}{\mathbb{e}}^{{- j}\;{\omega{({\tau + {\Delta\; t}})}}}} \right\rbrack}{\mathbb{e}}^{{- j}\;\omega\;\tau}}}}\ } \\{= {{N\left( {x,{\Delta\; t}} \right)} + {\frac{T\;{\mathbb{e}}^{j\;\omega\;\Delta\; t}}{2}{P(x)}}}}\end{matrix}\mspace{79mu}{{N\left( {x,{\Delta\; t}} \right)} = {\sum\limits_{\tau = 0}^{T - 1}{{I\left( {x,{\tau + {\Delta\; t}}} \right)}{\mathbb{e}}^{{- j}\;\omega\;\tau}}}}}} & (18)\end{matrix}$

In the case when linear transform Trans and reverse transform Trans⁻¹are defined between the watermark sequence w{w₁, . . . ,w_(L) }εC^(L)and P(x), when embedding digital watermark, P(x) is generated byP(x)=Trans(w)  (19)and, when detecting digital watermark,W′=Trans⁻¹(Q(x))  (20)is calculated, so that

$\begin{matrix}{w^{\prime} = {n + {\frac{T\;{\mathbb{e}}^{j\;\omega\;\Delta\; t}}{2}w}}} & (21)\end{matrix}$is obtained, wherein n=Trans⁻¹(N(x, Δt)).

As examples of linear transform Trans, for example, it may be atransform for simply arranging each value of w on the N−1-dimensionalspace sequentially, or it may be a transform for performing orthogonaltransform such as inverse Fourier transform and the like after arrangingeach value of w on the N−1-dimensional space sequentially.

By calculating complex correlation by applying arguments of precedingparagraphs, digital watermark detection and calculation of the amount Δtof desynchronization are available from the following equation.

$\begin{matrix}\begin{matrix}{\rho = {\omega^{\prime} \cdot \omega^{*}}} \\{= {\left( {n + {\frac{T\;{\mathbb{e}}^{{j\omega}\;\Delta\; t}}{2}\omega}} \right) \cdot \omega^{*}}} \\{\sim {\left( {\frac{T}{2}{\sum\limits_{k - 1}^{L}{w_{k}}^{2}}} \right){\mathbb{e}}^{j\;\omega\;\Delta\; t}}}\end{matrix} & (22)\end{matrix}$

(3) Detection by Difference (Differentiation) Correlation

In the above-mentioned detection scheme, instead of the calculation forobtaining Q(x), demodulation may be performed using f(t) based on thedifference or the differentiation of I″(x, t).

That is, when the signal is discrete, and assuming ΔI″(x, τ)=I″(x,τ+1)−I″(x, τ),

$\begin{matrix}\begin{matrix}{{Q(x)} = {\sum\limits_{\tau = 0}^{T - 1}{\Delta\;{I^{''}\left( {x,\tau} \right)}{f^{*}\ (\tau)}}}} \\{= {\sum\limits_{\tau = 0}^{T - 1}{\left\{ {{I^{''}\left( {x,{\tau + 1}} \right)} - {I^{''}\left( {x,\tau} \right)}} \right\}{f^{*}(\tau)}}}} \\{= \,{\left( {{N_{1}\left( {x,{\Delta\; t}} \right)} + {\frac{T\;{\mathbb{e}}^{j\;{\omega{({{\Delta\; t} + 1})}}}}{2}{P(x)}}} \right) -}} \\{\left( {{N_{0}\left( {x,{\Delta\; t}} \right)} + {\frac{T\;{\mathbb{e}}^{j\;{\omega\Delta}\; t}}{2}{P(x)}}} \right)} \\{= {\left( {{N_{1}\left( {x,{\Delta\; t}} \right)} - {N_{0}\left( {x,{\Delta\; t}} \right)}} \right) + {\frac{T\;{\mathbb{e}}^{j\;\omega\;\Delta\; t}}{2}{P(x)}\left( {{\mathbb{e}}^{j\;\omega} - 1} \right)}}}\end{matrix} & (23)\end{matrix}$In the equation,

${{N_{0}\left( {x,{\Delta\; t}} \right)} = {\sum\limits_{\tau = 0}^{T - 1}{{I\left( {x,{\tau + {\Delta\; t}}} \right)}{\mathbb{e}}^{{- j}\;\omega\;\tau}}}},{{N_{1}\left( {x,{\Delta\; t}} \right)} = {\sum\limits_{\tau = 1}^{T}{{I\left( {x,{\tau + {\Delta\; t}}} \right)}{\mathbb{e}}^{{- j}\;\omega\;\tau}}}}$and sincee^(jω)−1is known, similar detection is available.

In addition, for example, when the signal is continuous, similardetection is available by similar calculation using differentiation

$\frac{\mathbb{d}{I^{''}\left( {x,\tau} \right)}}{\mathbb{d}\tau}.$

For example, when considering a video signal and the like, it is knownthat correlation between frames of the signal is large. Since theshorter the time interval between two frames is, the higher correlationbetween the frames is, when difference between frames is calculated asmentioned above, original image components are largely canceled by equalto or greater than the amount of cancellation by the periodic signal,and an absolute value of the term N₁(x, Δt)−N₀(x, Δt) becomes verysmall, so that there is an advantage that energy of digital watermarkrelatively increases and detection becomes easy.

(4) Temporal Synchronization Unnecessary Digital Watermark when UsingArbitrary Periodic Signal:

Next, a case is considered in which arbitrary function f(t) is used as aperiodic signal and digital watermark is embedded by changing the phaseof the function. In this example, it is assumed that f(t) is a realfunction.

Embedding) A N-dimensional real number signal W(x, t) in which amplitudeand phase of f(t) are modulated by the absolute value and the argumentof P(x) is obtained.

For example, W(x, t)=|P(x)|f(t+s(x)) (24) is obtained. In this equation,

${s(x)} = {\frac{T}{2\pi}{{Arg}\left\lbrack {P(x)} \right\rbrack}}$in which T is the period of f(t).

By embedding W(x, t) into a signal I(x, t) that is an embedding subject,an embedded signal I′(x, t) is obtained.I′(x,t)=I(x,t)+W(x,t)  (25)

Detection) Considering a signal I″(x, t) in which I′(x, t) is shifted byΔt due to desynchronization.

$\begin{matrix}\begin{matrix}{{I^{''}\left( {x,t} \right)} = {I^{\prime}\left( {x,{t + {\Delta\; t}}} \right)}} \\{= {{I\left( {x,{t + {\Delta\; t}}} \right)} + {W\left( {x,{t + {\Delta\; t}}} \right)}}} \\{= {{I\left( {x,{t + {\Delta\; t}}} \right)} + {{{P(x)}}{f\left( {t + {\Delta\; t} + {s(x)}} \right)}}}}\end{matrix} & (26)\end{matrix}$

For I″(x, t) provided in a section 0≦t≦T, following integration iscalculated for performing demodulation using f(t) and f(t−π/4) in whichphase of f(t) is displaced by π/4.

$\begin{matrix}\begin{matrix}{{Q(x)} = {\int_{0}^{T}{{I^{''}\left( {x,\tau} \right)}\left\{ {{f(\tau)} + {{jf}\left( {\tau - \frac{\pi}{4}} \right)}} \right\}\ {\mathbb{d}\tau}}}} \\{= {{\int_{0}^{T}{{I\left( {x,{\tau + {\Delta\; t}}} \right)}\left\{ {{f(\tau)} + {{jf}\left( {\tau - \frac{\pi}{4}} \right)}} \right\}}} +}} \\{{{P(x)}}{f\left( {\tau + {\Delta\; t} + {s(x)}} \right)}\left\{ {{f(\tau)} + {{jf}\left( {\tau - \frac{\pi}{4}} \right)}} \right\}{\mathbb{d}\tau}} \\{= {{N\left( {x,{\Delta\; t}} \right)} + {{{P(x)}}{\int_{0}^{T}\left\{ {{{f\left( {\tau + {\Delta\; t} + {s(x)}} \right)}{f(\tau)}} +} \right.}}}} \\{\left. {{{jf}\left( {\tau + {\Delta\; t} + {s(x)}} \right)}{f\left( {\tau - \frac{\pi}{4}} \right)}} \right\}{\mathbb{d}\tau}}\end{matrix} & (27)\end{matrix}$In this equation,

${N\left( {x,{\Delta\; t}} \right)} = {\int_{0}^{T}{{I\left( {x,{\tau + {\Delta\; t}}} \right)}\left\{ {{f(\tau)} + {{jf}\left( {\tau - \frac{\pi}{4}} \right)}} \right\}\ {{\mathbb{d}\tau}.}}}$

This integration calculation is similar to calculation for obtainingautocorrelation of f( ) and following representation can be obtainedassuming that an autocorrelation function of f(t) is g(t).∫₀ ^(T) f(τ+Δt+s(x))f(τ)dτ=g(Δt+s(x))  (28)

$\begin{matrix}{{\int_{0}^{T}{{f\left( {\tau + {\Delta\; t} + {s(x)}} \right)}{f\left( {\tau - \frac{\pi}{4}} \right)}{\mathbb{d}\tau}}} = {g\left( {{\Delta\; t} + {s(x)} + \frac{\pi}{4}} \right)}} & (29)\end{matrix}$

Now, assuming

$\begin{matrix}{{h\left( {x,{\Delta\; t}} \right)} = {{g\left( {{\Delta\; t} + {s(x)}} \right)} + {{jg}\left( {{\Delta\; t} + {s(x)} + \frac{\pi}{4}} \right)}}} & (30)\end{matrix}$Q(x)=N(x, Δt)+|P(x)|h(x, Δt)  (31)

is obtained. In order to be able to perform digital watermark detectionsimilar to the before-mentioned example using a sine wave, it is onlynecessary that argument Arg[h(x, Δt)] of h(x, Δt) is a value close tothe phase of the embedded signal

$\frac{2\pi}{T}{\left( {{\Delta\; t} + {s(x)}} \right).}$

That is, it is only necessary to use a function h such that Δ_(Ψ)becomes small enough in

$\begin{matrix}{{{Arg}\text{[}{h\left( {x,{\Delta\; t}} \right\rbrack}} = {{\frac{2\pi}{T}\left( {{\Delta\; t} + {s(x)}} \right)} + {{\Delta\varphi}.}}} & (32)\end{matrix}$

At this time, product operation in complex correlation is represented asfollows.

$\begin{matrix}\begin{matrix}{{{{P(x)}}{{h\left( {x,{\Delta\; t}} \right)}}{\mathbb{e}}^{J\frac{2\pi}{T}{({{\Delta\; t} - {s{(x)}} + {\Delta\varphi}})}}{P^{*}(x)}} = {{{P(x)}}{\mathbb{e}}^{J\frac{2\pi}{T}{s{(x)}}}{P^{*}(x)}{{h\left( {x,} \right.}}}} \\{{\left. {\Delta\; t} \right)}{\mathbb{e}}^{{J\frac{2\pi}{T}\Delta\; t} + {\Delta\varphi}}} \\{= {{{P(x)}}^{2}{{h\left( {x,{\Delta\; t}} \right)}}{\mathbb{e}}^{{J\frac{2\pi}{T}\Delta\; t} + {\Delta\varphi}}}}\end{matrix} & (33)\end{matrix}$A total sum of this is obtained as a complex correlation value, and itcan be obtained within a range of an error according to the amount Δt ofdesynchronization and Δ_(Ψ) from the argument of the complex correlationvalue.

In the calculation,

${P^{*}(x)} = {{{P(x)}}{\mathbb{e}}^{J\frac{2\pi}{T}{s{(x)}}}}$is used. In addition, for the sake of easy understanding, an example wasshown in which linear transform Trans is omitted and correlationoperation is directly performed by P(x).

The above discussions indicate that Δ_(Ψ)=0 holds true when the periodicsignal is the sine wave, and on the other hand, Δ_(Ψ)≠0 holds true whenthe periodic signal is other than the sine wave, which means that erroroccurs in measurement of the amount Δt of desynchronization.

(5) Examples of Periodic Signals

As the periodic signal, it is only necessary to use a periodic functionhaving following characteristics.

1) Result of integrating the periodic function for one period becomes 0.

2) Autocorrelation function does not have a sharp peak.

The condition of 1) may be expressed as follows, for example.∫₀ ^(T) f(t)dt=0  (34)In the equation, T is a period of the periodic function.

As the condition of 2), a condition “a value of second-order derivativein the vicinity of the vertex of the autocorrelation function does notagree with a sign of the vertex”.

FIGS. 4A-C show examples of periodic signals. The periodic signals shownin the figures are (FIG. 4A) (a) sine wave, (FIG. 4B) (b) triangularwave, and (FIG. 4 c)(c) rectangular wave, and each signal can berepresented by equations as follows in a range of 0≦t<T (T is a periodof the signal). By the way, the periodic signal is not limited to theseexamples, and it is needless to say that any periodic signal having theabove-mentioned characteristics can be used.

$\begin{matrix}{y = {a\;\sin\;\omega\; t}} & (a) \\{y = \left\{ \begin{matrix}{{{- \frac{4\; a}{T}}t} + a} & \left( {0 \leq t < \frac{T}{2}} \right) \\{{\frac{4\; a}{T}t} - {3\; a}} & \left( {\frac{T}{2} \leq t < T} \right)\end{matrix} \right.} & (b) \\{y = \left\{ \begin{matrix}a & \left( {0 \leq t < \frac{T}{2}} \right) \\{- a} & \left( {\frac{T}{2} \leq t < T} \right)\end{matrix} \right.} & (c)\end{matrix}$

The condition of 1) indicates that direct current component of tdirection of I″(x, t) can be canceled as a result of integration whendetection.

Meaning of the condition of 2) is described as follows.

FIGS. 5A-C shows autocorrelation functions of each periodic signal ofFIGS. 4A-C. In addition, FIGS. 6A-C show locus of the complex functionh( ) on the complex plane for each periodic signal.

(FIG. 5A, FIG. 6A) In the example of sine wave, the autocorrelationfunction changes smoothly, so that the locus of h( ) becomes a circle.In this case, Δ_(Ψ)=0 holds true, and this means that the amount Δt ofdesynchronization can be obtained with high accuracy.

(FIG. 5B, FIG. 6B) In the example of triangular wave, autocorrelationfunction change smoothly in the same way, and the value of second-orderderivative in the vicinity of the vertex is different from the sign ofthe vertex (a value of second-order derivative in the vicinity of thevertex whose sing is plus is minus and the signs are not the same), andit is an autocorrelation function that does not have a sharp peak. As aresult, the locus of h( ) becomes almost the same as a circle, and Δ_(Ψ)becomes small enough, so that it means that the amount Δt ofdesynchronization can be obtained with high accuracy.

(FIG. 5C, FIG. 6C) In the example of the rectangular wave, although theautocorrelation function is not smooth, the value of second-orderderivative in the vicinity of the vertex is different from the sign ofthe vertex (the value of the second-order derivative in the vicinity ofthe vertex whose sign is plus is 0, so the signs are not the same).Thus, the autocorrelation function has no sharp peak in the same way. Asa result, the locus of h( ) does not becomes a circle, but becomes arhombus, and Δ_(Ψ)becomes a relatively small value, which means that theamount Δt of desynchronization can be obtained with high accuracy tosome extent.

Generally, since calculation for the value of the rectangular wave orthe triangular wave can be performed at higher speed compared with thecalculation for the value of the sine wave, high speed digital watermarkdetection becomes possible as a whole at the sacrifice of some error ofthe amount of desynchronization by using a periodic function, instead ofthe sine wave, that satisfies the above conditions such as thetriangular wave and the rectangular wave. For example, it is especiallyeffective when performing digital watermark detection using very limitedcomputational resources like digital watermark detection using aportable terminal such as a cellular phone, and when high speedprocessing is required in the case of performing large amount of digitalwatermark detection.

(6) Temporal Synchronization Unnecessary Digital Watermark Detectionwhen Using Orthogonal Two Periodic Functions:

Next, a case is considered in which two orthogonal periodic functionsf₁(t) and f₂(t) having a same basic frequency are used as the periodicsignal.

This case corresponds to a case in which f(t)=f₁(t)+jf₂(t) is used asthe periodic complex function f(t) in the above-mentioned description oftemporal synchronization unnecessary digital watermark based on temporaldirection single frequency embedding.

For example, assuming that f₁(t) is a rectangular wave of period 4 andf₂(t) is a triangular wave of period 4, and that they are defined assignals shown in FIGS. 7A and B, respectively.

At this time, each of f₁(t) and f₂(t) has a basic frequency 1/4, andintegration for one period is as follows,∫₀ ^(T) f ₁(t)f ₂(t)dt=0  (35)which indicates they are orthogonal, wherein T is a signal period, andit is T=4 in this example.

In this case, for example, when P(x₀, T)=1+0_(j) for x=x₀, correspondingW(x₀, t) becomes the same as f₁(t) in FIG. 7A.

When there is no desynchronization, a signal G₁(t) shown in FIG. 8Awhich is described by removing original image components is obtainedwhen performing detection. As a result of correlation calculationbetween this and f₁(t), f₂(t),∫₀ ^(T) G ₁(t)f ₁(t)dt=4  (36)∫₀ ^(T) G ₂(t)f ₂(t)dt=0  (37)hold true, and Q(x₀)=4+0_(j).

When the phase is shifted by 90 degrees due to desynchronization, asignal G₂(t) shown in FIG. 8B which is described by removing originalimage components is obtained when performing detection. As a result ofcorrelation calculation between this and f₁(t), f₂(t),∫₀ ^(T) G ₂(t)f ₁(t)dt=0  (38)

$\begin{matrix}{{\int_{0}^{T}{{G_{2}(t)}{f_{2}(t)}\ {\mathbb{d}t}}} = \frac{4}{3}} & (39)\end{matrix}$are obtained, and

${Q\left( x_{0} \right)} = {0 + {\frac{4}{3}j}}$is obtained.

Similarly considering, according to the size of desynchronization, Q(x₀)changes following a locus 1 on the complex plane shown in FIG. 9.

In addition, for example, when P(x₁)=0+1_(j) for x=x₁, correspondingW(x₁, t) becomes the same as f₂(t) shown in FIG. 7B. And, based on thesimilar consideration, according to the size of desynchronization, Q(x₁)changes following a locus 2 on the complex plane shown in FIG. 9.

The argument of Q(x) can be obtained by calculation similar tobefore-mentioned calculation of the complex correlation value, and theamount Δt of desynchronization can be obtained, from the argument of thecomplex correlation value, within a range of error determined bycalculation.

As mentioned above, also when using orthogonal two periodic functionsf₁(t) and f₂(t) having a same basic frequency as the periodic function,the amount of desynchronization can be obtained as a whole at thesacrifice of some error.

[First Embodiment]

FIG. 10 shows configurations of a digital watermark embedding apparatusand a digital watermark detection apparatus according to a firstembodiment of the present invention.

<Digital Watermark Embedding Apparatus>

First, the digital watermark embedding apparatus is described.

The digital watermark embedding apparatus 100 includes a complex patterngeneration unit 110, a temporal modulation unit 130, an embeddingpattern superimposing unit 140, a first storage unit 150, and a secondstorage unit, and the apparatus receives embedding information 911 andbefore-embedding signal 912, and outputs embedded signal 923.

In the following, operation of the digital watermark embedding apparatus100 is described.

FIG. 11 is a flowchart showing operation of the digital watermarkembedding apparatus according to a first embodiment of the presentinvention. Digital watermark embedding processing by the digitalwatermark embedding apparatus 100 is performed by the followingprocedure.

Step 100) The complex pattern generation unit 110 generates an embeddingcomplex pattern 921 based on received embedding information 911, andstores it into the first storage unit 150 such as a memory.

The embedding complex pattern 921 is a N−1-dimensional pattern composedof complex numbers, and represents content of embedding information.Details of operation of the complex pattern generation unit 110 aredescribed later with reference to FIG. 12.

By the way, as shown in after-mentioned other method for embedding intocomplex numbers, it is possible to configure the N−1-dimensional patternas a pattern of real number values depending on processing of thetemporal modulation unit 130.

Step 110) The temporal modulation unit 130 generates an embeddingpattern 922 based on the embedding complex pattern that is generated bythe complex pattern generation unit 110 and is stored in the firststorage unit 150, and stores the embedding patter 922 into the secondstorage unit 160 such as a memory. The embedding pattern 922 isgenerated as N-dimensional pattern, that is configured by real numbervalues, by performing modulation in time axis direction on the embeddingcomplex pattern 921.

Details of operation of the temporal modulation unit 130 is describedlater.

Step 120) The embedding pattern superimposing unit 140 superimposes theembedding pattern 922, that is generated by the temporal modulation unit130 and that is stored in the second storage unit 160, on the inputbefore-embedding signal 912, and outputs an embedded signal 923.

Details of operation of the embedding pattern superimposing unit 140 aredescribed later.

<Digital Watermark Embedding Apparatus—Complex Pattern Generation Unit>

FIG. 12 shows a configuration example of the complex pattern generationunit of the first embodiment of the present invention.

The complex pattern generation unit 110 a includes an embedding sequencegeneration unit 111 and a complex array generation unit 112, and theunit receives the embedding information 911 and outputs the embeddingcomplex pattern 921.

Processing of generation of the embedding complex pattern by the complexpattern generation unit 110 a is performed by the following procedure.

FIG. 13 is a flowchart showing processes of the complex patterngeneration unit of the first embodiment of the present invention.

Step 101) The embedding sequence generation unit 111 generates anembedding sequence 913 that is a sequence of numbers indicatingembedding information based on received embedding information 911.Details of operation of the embedding sequence generation unit 111 aredescribed later.

Step 102) The complex array generation unit 112 assigns the embeddingsequence 913 generated by the embedding sequence generation unit 111 toa real part and an imaginary part of each elements of a N−1-dimensionalcomplex array to generate the embedding complex pattern 921 and storesit to the first storage unit 150. Details of the complex arraygeneration unit 112 are described later.

<Digital Watermark Embedding Apparatus—Embedding Sequence GenerationUnit>

The embedding sequence generation unit 111 generates the embeddingsequence 913 according to the following processes.

Generation of the embedding sequence 913 can be performed by a methodsimilar to a configuration method for an embedding sequence shown in thepatent document 1, —Takao Nakamura, Hiroshi Ogawa, Atsuki Tomioka,Youichi Takashima, “An Improvement of Watermark Robustness against.Moving and/or cropping the area of the Image”, The 1999 Symposium onCryptography and Information Security, SCIS99—W3-2.1, pp. 193-198,1999—, or —Takao Nakamura, Atsushi Katayama, Masashi Yamamuro, NoboruSonehara, “Fast Watermark Detection Scheme from Analog Image forCamera-equipped Cellular Phone”, IEICE Transactions D-II, Vol. j87-D-II,No. 12, pp. 2145-2155, 2004—.

In the following, as an example of embedding information 911,

-   -   An example indicating only a fact that digital watermark is        embedded;    -   An example of information of 1 bit;    -   A first example of information of n bits;    -   A second example of information of n bits;        are described. By the way, the method is not limited to these        examples, and other methods for generating embedding sequence        may be used.

EXAMPLE 1

When the embedding information 911 indicates only a fact that “digitalwatermark is embedded”, the embedding sequence 913 may be calculated asa number sequence represented using a pseudo-random number sequence.That is, assuming that a pseudo-random number sequence of average 0 isPN={PN₁, PN₂, . . . , PN_(L)} (L indicates a length of the sequence),the embedding sequence w={w₁, w₂, . . . , w_(L)} may be determined asw=PN={PN₁, PN₂, . . . , PN_(L)}   (40).

In addition, as the pseudo-random number sequence, M sequences or GOLDsequences may be used.

EXAMPLE 2

When the embedding information 911 is information of 1 bit, theembedding sequence 913 may be calculated as a number sequence obtainedby performing spectrum spreading on the information of 1 bit using apseudo-random number sequence. That is, assuming that the embeddinginformation is b and that the pseudo-random number sequence is PN={PN₁,PN₂, . . . , PN_(L) } (L is a length of the sequence), the embeddingsequence w={w₁, w₂, . . . , w_(L)} may be determined as follows.

$\begin{matrix}{w = \left\{ \begin{matrix}{{PN} = \left\{ {{PN}_{1},{PN}_{2},\ldots\mspace{14mu},{PN}_{L}} \right\}} & \left( {{{if}\mspace{14mu} b} = 1} \right) \\{{- {PN}} = \left\{ {{- {PN}_{1}},{- {PN}_{2}},{\ldots\mspace{14mu} - {PN}_{L}}} \right\}} & \left( {{{if}\mspace{14mu} b} = 0} \right)\end{matrix} \right.} & (41)\end{matrix}$

In addition, as the pseudo-random number sequence, M sequences or GOLDsequences may be used, for example.

EXAMPLE 3

When the embedding information 911 is information composed of n bits,the embedding sequence 913 may be calculated by multiplexing numbersequences obtained by performing spectrum spreading by using thepseudo-random sequence on each symbol that is obtained by dividinginformation of n bits into groups of m bits, for example. That is,following procedure may be performed.

FIG. 14 is a flowchart of detailed operation of the embedding sequencegeneration unit of the first embodiment of the present invention.

Step 201) The embedding information 911 of n bits are divided into aplurality of symbols S₁, S₂, . . . , S_(k). Every symbol may be the samem bits, or each symbol may represent information of different number ofbits.

In this process, each “symbol” represents a part of embeddinginformation, and is information that is a unit for actual digitalwatermark processing. For example, when the embedding information 911 isprovided as a binary number of 64 bits length, it may be divided intopieces of information each having 12 bits so that each of 12 bitsinformation may be the symbol as shown in FIG. 15. Alternatively, onesymbol may represents information of 1 bit. Like the example shown inFIG. 15, when the length of the embedding information 911 (64 bits inthis example) cannot be divided by the length (12 bits) of each symbol,a part of bits in a part (last symbol in this example) of symbols may bepadded with fixed values (0 in this example).

Step 202) Spectrum spreading is performed on each symbol obtained instep 201 to generate a spread sequence P₁, . . . , P_(k) correspondingto each symbol.

As a method for spectrum spreading, there is a following method, forexample.

For example, when one symbol represents information of 1 bit, k PNsequences PN₁=(pn₁₁, pn₁₂, . . . ,), . . . PN_(k)=(pn_(k1), pn_(k2), . .. ) each having a value of {1, −1} are generated for each symbol S₁,S_(k), and when the value of the symbol for symbol i represents bit 1,PN_(i) may be used as the spread sequence P_(i), and when the value ofthe symbol represents bit 0, −PN_(i) may be used as the spread sequenceP_(i).

In addition, when one symbol represents information of 12 bits, 4096 PNsequences PN_((1, 0)), . . . , PN_((1, 4095)), PN_((2, 0)) . . .PN_((k, 4095)), may be prepared for each symbol, and when the value ofsymbol i indicates an integer value x by the 12 bits, PN_((i, x)) may beused as spread sequence P_(i).

In addition, as PN sequence (pseudo-random number sequence), M sequencesor GOLD sequences may be used.

Step 203) The embedding sequence w is calculated from the spreadsequence P_(i) as follows.

$\begin{matrix}{w = {\frac{1}{\sqrt{L}}{\sum\limits_{i = 1}^{k}\; P_{l}}}} & (42)\end{matrix}$For example, in the latter example in step 202, w is represented asfollows.

$\begin{matrix}{w = \left\{ {{\frac{1}{\sqrt{L}}{\sum\limits_{i = 1}^{k}{PN}_{({1,S_{l}})}}},{\frac{1}{\sqrt{L}}{\sum\limits_{i = 1}^{k}{PN}_{({2,S_{i}})}}},\ldots\mspace{14mu},{\frac{1}{\sqrt{L}}{\sum\limits_{i = 1}^{k}{PN}_{({L,S_{i}})}}}} \right\}} & (43)\end{matrix}$In the above equation, the reason for using

$\frac{1}{\sqrt{L}}$for multiplication is that a standard deviation of each element of thesequence becomes 1, but, it is not necessary to multiply

$\frac{1}{\sqrt{L}}$when embedding strength is properly controlled in calculations afterthat.

EXAMPLE 4

When the embedding information 911 is information configured by n bits,the embedding sequence 913 may be calculated by directory performingspectrum spreading using the pseudo-random number into three timeslength of the n bits information. That is, the calculation may beperformed based on the following procedure.

1) Assuming that n bits embedding information 911 is b₀, b₁, b₂, . . . ,b_(n), a sequence S is obtained by repeating each bit m times, whereineach bit b_(i) is a value of +1 or −1.

$\begin{matrix}{S = {\underset{\underset{m}{︸}}{b_{0}b_{0}\mspace{14mu}\ldots\mspace{14mu} b_{0}}\underset{m}{\underset{︸}{b_{1}b_{1}\mspace{14mu}\ldots\mspace{14mu} b_{1}}}\underset{m}{\underset{︸}{b_{2}b_{2}\mspace{14mu}\ldots\mspace{14mu} b_{2}}}b_{3}\mspace{14mu}\ldots\mspace{14mu} b_{n - 1}\underset{m}{\underset{︸}{b_{n}b_{n}\mspace{14mu}\ldots\mspace{14mu} b_{n}}}}} & (44)\end{matrix}$

2) S is spread using a pseudo-random number sequence PN={PN₁, PN₂, . . ., PN_(mn)} having {+1, −1} to obtain the embedding sequence w. That is,when w={w₁, w₂, . . . w_(mn)},w₁=b₀PN₁b₀PN₂ . . . b₀PN_(m)  (45)

(representing that first bit is b₀×PN₁, second bit is b₀×PN₁ . . . , andso forth)

$\begin{matrix}{w_{2} = {b_{1}{PN}_{m + 1}\mspace{14mu} b_{1}{PN}_{m + 2}\mspace{14mu}\ldots\mspace{14mu} b_{1}{PN}_{2m}}} \\\vdots \\{w_{mn} = {b_{n}{PN}_{{{({m - 1})}n} + 1}\mspace{14mu} b_{n}{PN}_{{{({m - 1})}n} + 2}\mspace{14mu}\ldots\mspace{14mu} b_{n}{PN}_{mn}}}\end{matrix}$

Such a method for generating the embedding sequence is also described inTakao Nakamura, Atsushi Katayama, Masashi Yamamuro, Noboru Sonehara,“Fast Watermark Detection Scheme from Analog Image for Camera-equippedCellular Phone”, IEICE Transactions D-II, Vol. j87-D-II, No. 12, pp.2145-2155, 2004.

<Digital Watermark Embedding Apparatus—Complex Array Generation Unit>

The complex array generation unit 112 in the embedding complex patterngeneration unit 110 a generates a complex pattern 921 by the followingprocesses.

Operation of the complex array generation unit 112 of the complexpattern generation unit 110 a is shown in the following.

FIG. 16 is a flowchart of the operation of the complex array generationunit in the first embodiment of the present invention.

Step 301) N−1-dimensional complex array, having a size M₁×M₂× . . .M_(N−1), in which every element value is 0 is prepared, wherein M₁, M₂,. . . , M_(N−1) are predetermined element numbers.

Step 302) Values are extracted from the embedding sequence 913 two bytwo in sequence, then, from a position (0, 0, . . . ,0) of the arrayprepared in step 301 in sequence, the extracted values are set in thearray such that the extracted values become the real part and theimaginary part of the element value. That is, when the complex array isrepresented as A[p₁, p₂, . . . , p_(N−1)] (p_(n)≧0) and the embeddingsequence 913 is represented as w₁, w₂, . . . , w_(L),A[0, 0, . . . , 0]=w ₁ +jw ₂A[1, 0, . . . , 0]=w ₃ +jw ₄  (46)wherein j represents the imaginary unit.

FIG. 17 shows this manner. FIG. 17 shows an example of two dimensionalcomplex array.

Step 303) The complex array generated in step 302 is output as theembedding complex pattern 921.

Accordingly, by generating the N−1-dimensional embedding complex pattern921 as a complex array based on the embedding sequence 913 that isgenerated using pseudo-random number sequence, each element value of theembedding complex pattern 921 is determined such that it extends overthe complex number space. As a result, phases in the embedding pattern922 that is obtained as a result of after mentioned temporal modulationare spread such that they are different according to positions on theN−1-dimensional space, so that the size of nose components that appeardue to the before-embedding signal 912 when detecting digital watermarkbecomes smaller.

In addition, before performing the procedure of step 302, order of theembedding sequence 913 may be permuted to random order using apseudo-random number. By doing this, attacks such as invalid analysis ofembedded information and rewriting become difficult, and in addition tothat, it has effects as interleave coding, which contributes topreventing locally imbalance of robustness. In that case, a value of aseed of the pseudo-random number that is used for permuting the order isprovided as a key for digital watermark embedding, so that the same keyis used for digital watermark detection.

In addition, instead of permuting the order on the embedding sequence913, elements of the complex array obtained in step 302 may be permuted.

<Digital Watermark Embedding Apparatus—Temporal Modulation Unit>

In the following, operation of the temporal modulation unit 130 isdescribed in detail.

FIG. 18 is a configuration example of the temporal modulation unit inthe first embodiment of the present invention.

A temporal modulation unit 130 a includes a periodic signal generationunit 131, modulation units 132, and an adding unit 133, and it receivesan embedding complex pattern 921 and outputs an embedding pattern 922.

Processes for generating the embedding pattern 922 by the temporalmodulation unit 130 a are performed according to the followingprocedure.

FIG. 19 is a flowchart of operation of the temporal modulation unit inthe first embodiment of the present invention.

Step 401) The periodic signal generation unit 131 generates two periodicsignals that have the same basic frequency and that are orthogonal. Forexample, two periodic signals may be generated based on one periodicsignal such that the periods are different by 90 degrees, that is, 1/4period. Examples of periodic signals to be generated are describedlater.

Step 402) The modulation units 132 modulates each of the real part andthe imaginary part of the received embedding complex pattern 921 in thetemporal direction using the two periodic signals generated in step 401.Concrete examples for modulation are described later.

Step 403) The adding unit 133 adds the two N-dimensional signalsmodulated in the modulation units 132 to obtain the embedding pattern922 and stores it into the second storage unit 160.

Examples of the periodic signals generated in step 401 are described.

The periodic signal generated by the periodic signal generation unit 131is (FIG. 4A) (a) sine wave, (FIG. 4B)(b) triangular wave, or (FIG. 4C)(c) rectangular wave, and each signal is represented by an equation in arange of 0≦t<T (T is a period of the signal) as follows.

$\begin{matrix}{y = {a\;\sin\;\omega\; t}} & (a) \\{y = \left\{ \begin{matrix}{{{- \frac{4a}{T}}t} + a} & \left( {0 \leq t < \frac{T}{2}} \right) \\{{\frac{4a}{T}t} - {3a}} & \left( {\frac{T}{2} \leq t < T} \right)\end{matrix} \right.} & (b) \\{y = \left\{ \begin{matrix}a & \left( {0 \leq t < \frac{T}{2}} \right. \\{- a} & \left( {\frac{T}{2} \leq t < T} \right)\end{matrix} \right.} & (c)\end{matrix}$Details of the periodic signals were as described before.

Next, modulation in the modulation unit 132 is performed by performingAM modulation on the periodic signals, as carriers, generated by theperiodic signal generation unit 131 using the values of the real partand the imaginary part of the value of each position of theN−1-dimensional complex pattern 921 so that the periodic signals areconverted to N-dimensional pattern.

That is, more specifically, following processes are performed, forexample.

Assuming that N−1 dimensional complex pattern is represented as P(x₁,x₂, . . . , x_(N−1)). When the real part and the imaginary part arerepresented as P_(r) and P_(i) respectively, and the pattern isrepresented asP(x ₁ , x ₂ , . . . , x _(N−1))=P _(r)(x ₁ , x ₂ , . . . , x _(N−1))+j·P_(i)(x ₁ , x ₂ , . . . , x _(N−1))(47)wherein j is the imaginary unit.

Assuming that two periodic signals f_(r)(t) and f_(i)(t) are generatedby the periodic signal generation unit 131. In this example, it isassumed that f_(r) and f_(i) are generated from a same periodic signalsuch that the phase is different by 90 degrees, as shown inf_(i)(t)=f_(r)(t−T/4) (48), wherein T is a period of the periodicsignal.

N-dimensional patterns W_(r) and W_(i) are obtained by modulating P_(r)and P_(i) using f_(r)(t) and f_(i)(t) respectively as shown in thefollowing equation.W _(r)(x ₁ , x ₂ , . . . , x _(N−1) t)=P _(r)(x ₁ , x ₂ , . . . , x_(N−1))×f _(r)(t)  (49)W _(i)(x ₁ , x ₂ , . . . , x _(N−1) , t)=P _(i)(x ₁ , x ₂ , . . . , x_(N−1))×f _(i)(t)  (50)

In step 403, these W_(r) and W_(i) are added so that followingN-dimensional signal w is obtained as the embedding pattern 922.W(x ₁ , x ₂ , . . . , x _(N−1) , t)=W _(r)(x ₁ , x ₂ , . . . , x _(N−1), t)+W _(i)(x ₁ , x ₂ , . . . , x _(N−1) ,t)  (51)

In the following, an example is shown in which a sine wave is used asthe periodic signal for an video signal of N=3.

Assuming that,f _(r)(t)=cos ωt  (52)f _(i)(t)=sin ωt  (53)W(x, y, t)=P _(r)(x,y)cos ωt+P _(i)(x,y)sin ωt  (54)is obtained, wherein ω is angular velocity for the period T, that is,ω=2π/T.

It is needless to say that these calculations can be performed asfollows using a complex function f(t)=e)^(jωt)=cos ωt+j sin ωt.W(x, y, t)=

[P(x, y)×f ^((*))(t)]=

[P(x, y)e ^(−eωt)]  (55)In the equation, f^((*))(t) is a conjugate complex number of f(t), and

[C]is calculation for extracting the real part of C.

<Digital Watermark Embedding Apparatus—Embedding Pattern SuperimposingUnit>

In the following, operation of the embedding pattern superimposing unit140 is described in detail.

The embedding pattern superimposing unit 140 adds the N-dimensionalembedding pattern 922 that is generated by the temporal modulation unit130 a and that is stored in the second storage unit 160 to theN-dimensional signal received as the before-embedding signal 912 so asto superimpose the N—dimensional embedding pattern 922 on theN-dimensional signal, and outputs the N-dimensional signal that is aresult of the superimposing as an embedded signal 923.

Embedding strength) When adding the embedding pattern 922, it may beembedded by being strengthened using a predetermined strength parameterα. That is, assuming that N-dimensional before-embedding signal 912 isI(x₁, x₂, . . . , x_(N−1), t) and that the embedding pattern 922 isW(x₁, x₂, . . . , x_(N−1), t), the embedded signal 923 I′(x₁, x₂, . . ., x_(N−1), t) is obtained byI′(x ₁ , x ₂ , . . . , x _(N−1) ,t)=I(x ₁ , x ₂ , . . . , x _(N−1) ,t)+α·W(x ₁ , x ₂ , . . . , x _(N−1) , t)  (56).

The strength parameter α maybe configured so as to change according tocharacteristics amount calculated from the whole of the before-embeddingsignal 912 or from a part that is a subject for calculation in thebefore-embedding signal 912. For example, when the before-embeddingsignal 912 is the video signal, it may be configured such that embeddingis performed strongly (that is, such that α is a large value) for apart, in which the added embedding pattern is hardly prominent, such asa texture region or heavy movement region in a frame image, and suchthat embedding is performed weekly (that is, such that α is a smallvalue) for a part, in which the added embedding pattern becomesprominent, such as a flat region or a slow and even movement region in aframe image.

Repetition of embedding pattern) When superimposing the embeddingpattern, when the size of the before-embedding signal 912 is greaterthan the size of the embedding pattern 922, the embedding pattern 922may be added by repeating it.

Following are examples of the case in which the size of thebefore-embedding signal 912 is greater than the size of the embeddingpattern 922.

1) When the before-embedding signal 912 is a video signal, when thelength (number of frames) of the before-embedding signal 912 in the timedirection is longer than the time length of the embedding pattern, theembedding pattern 922 may be repeated a plurality of times as shown inFIG. 20.

2) When the before-embedding signal 912 is a video signal, when the sizeof the frame image (angle of view) of the before-embedding signal 912 isgreater than the size of the frame image (angle of view) of theembedding pattern 922, the embedding pattern 922 may be added such thatit is paved like tiles vertically and horizontally as shown in FIG. 21.

Enlargement of embedding pattern) In addition, before superimposing theembedding pattern, the embedding pattern 922 may be enlarged into anarbitrary size, or enlarged such that the size becomes equal to the sizeof the before-embedding signal 912. FIG. 22 shows the example. In FIG.22, an example of two times enlargement, and an example in which thepattern is enlarged to fit the size of the before-embedding signal 912are shown. But, it is needless to say that it may be enlarged to a sizeother than those.

Any algorithm may be used for enlargement. As shown in FIG. 22,enlargement may be performed such that enlarged one block corresponds toone value and the block after enlargement is made to include all samevalues, or a known interpolation method such as linear interpolation andbi-cubic may be used.

In FIG. 22, when the before-embedding signal 912 is a video signal,although an example is shown in which enlargement is performed in spacedirection in units of frame images, it is needless to say thatenlargement may be performed also in the time direction.

Embedding into characteristics amount) In addition, when superimposingthe embedding pattern 922 on the before-embedding signal 912, instead ofdirectly adding values of the embedding pattern 922 to the signal valuesof the before-embedding signal 912, superimposing may be performed bychanging the before-embedding signal 912 such that predeterminedcharacteristics amount of the before-embedding signal 912 is changed bythe value of the embedding pattern 922 or by scalar times of theembedding pattern 922.

As an example of the characteristics amount, there are signal values ofthe before-embedding signal 912 or the average value of signal valuesfor each block. When the before-embedding signal 912 is the video signalor the image signal, brightness, color difference, and color signalvalue of RGB of the pixel of the video or image may be used.

<Digital Watermark Detection Apparatus>

The digital watermark detection apparatus 200 shown in FIG. 10 includesa temporal demodulation unit 210, a detection information extractionunit 220 and a pattern storage unit 250, and it receives the embeddedsignal 923 and outputs detection information 914.

In the following, operation of the digital watermark detection apparatus200 is described.

FIG. 23 is a flowchart of operation of the digital watermark detectionapparatus in the first embodiment of the present invention.

Step 501) The temporal demodulation unit 210 performs demodulation inthe time axis direction based on the input embedded signal 923 to obtaina detection complex pattern 961, and stores it into the pattern storageunit 250. The detection complex pattern 961 is a N−1-dimensional patterncomprised of complex numbers. Details of operation of the temporaldemodulation unit 210 are described later.

By the way, before performing temporal demodulation processing by thetemporal demodulation unit 210, processes such as geometricaldeformation correction, nose removal, filtering, block superimposing,and block dividing may be performed by pre-processing for the embeddedsignal 923. These examples are described later.

Step 502) The detection information extraction unit 220 analyzes thedetection complex pattern 961 that is obtained by the temporaldemodulation unit 210 and is stored in the pattern storage unit 250,extracts digital watermark information embedded by the digital watermarkembedding apparatus 100 to output it as detection information 914.

Details of operation of the detection information extraction unit 220are described later.

By the way, before performing detection information extractionprocessing by the detection information extraction unit 220, processessuch as geometrical deformation correction, nose removal, filtering,block superimposing, and block dividing in N−1-dimensional space, forexample, may be performed by pre-processing for the detection complexpattern 961. These examples are described later.

<Pre-processing for Embedded Signal>

In the following, examples of pre-processing for the embedded signal 923in the digital watermark detection apparatus 200 is described.

Geometric deformation correction) In the case when geometricaldeformation such as enlargement, compression, rotation, translation,aspect ratio change and projective transformation is applied to theembedded signal 923 in which digital watermark is embedded in thedigital watermark embedding apparatus 100, there is a case in whichdetection of digital watermark becomes difficult without modification.Thus, pre-processing may be performed for correcting this.

As for the geometric deformation correction, as shown in adocument—Csurka, G., Deguillaume, F., Ruanaidh, J. J. K. O, and Pun, T.,“A Bayesian Approach to Affine Transformation Resistant Image and VideoWatermarking,” Information Hiding, Proceedings Lecture Notes in ComputerScience 1768, pp. 270-285, Springer-Verlag (2000)—, for example, asignal for performing geometric correction is embedded in the signalseparately from digital watermark information, and degree of changeapplied to the signal is estimated by detecting this, so that correctionmay be performed by performing reverse conversion of the estimatedchange for the signal. In addition, for example, as shown in adocument—Honsinger, C., “Data Embedding using Phase Dispersion, “IEESeminar on Secure Images and Image Authentication (Ref. No. 2000/039),pp. 5/1-5/7 (2000)—, a periodic pattern having repetition may be used asthe embedding pattern itself that has embedding information as digitalwatermark, enlargement/compression ratio is calculated by observingchange of the period based on autocorrelation function when performingdetection, so that correction may be performed by performing reverseconversion of the change based on the obtained enlargement/compressionratio. In addition, for example, when the subject signal is an image ora video, a rectangular area in the image may be extracted, and geometriccorrection may be performed as if digital watermark is embedded in thearea using a method like one shown in—Atsushi KATAYAMA, Takao NAKAMURA,Masashi YAMAMURO, Noboru SONEHARA, “A New High-Speed Corner DetectionMethod: Side Trace Algorithm (STA) for i-appli to Detect Watermarks”IEICE Transactions D-II, Vol. j88-D-II, No. 6, pp. 1035-1046, 2005—.

Filter processing) When noise is added to the embedded signal 923 inwhich digital watermark is embedded, filter processing for removing thenoise may be applied, and filter processing that can remove componentsof original before-embedding signal while reserving signal components ofdigital watermark.

Block superimposing) In the digital watermark embedding apparatus 100,when the embedding pattern superimposing unit 140 adds the embeddingpattern 922 such that it is repeated when the size of thebefore-embedding signal 912 is greater than the size of the embeddingpattern 922, block superimposing processing may be performed so as todivide the embedded signal 923 into each part of the repeated pattern,superimpose and add these to bring together them into one block.

Change to block) In the digital watermark embedding apparatus 100, whenthe embedding pattern superimposing unit 140 enlarges the embeddingpattern 922 when the size of the before-embedding signal 912 is greaterthan the size of the embedding pattern 922, digital watermark detectionmay be performed after contracting the embedded signal 923.

Detection from characteristics amount) In the digital watermarkembedding apparatus 100, when superimposing the embedding pattern on thebefore-embedding signal 912, when superimposing is performed by changingthe before-embedding signal 912 such that the predeterminedcharacteristic amount of the before-embedding signal 912 is changed bythe value of the embedding pattern 922 or by scalar times, digitalwatermark detection may be performed based on information obtained bycalculating a predetermined characteristic amount from the embeddedsignal 923.

For example, as shown in FIG. 24, the embedded signal 923-1 may bedivided into blocks so as to configure lines of characteristic amount bycalculating characteristic amount of each block so that digitalwatermark may be detected from this. As an example of the characteristicamount, an average of signal values in the block may be used, forexample. In addition, when the signal is a video signal or an imagesignal, brightness or color difference of the pixel of the video or theimage, or color signal value of RGB may be used.

Pre-processing described in these examples may be performed on thedetection complex pattern 961 as pre-processing of the detectioninformation extraction processing in the detection informationextraction unit 220. Especially, as to the geometric deformationcorrection, when the axis of N-th dimension is time in the video signal,by correcting expansion and contraction in the time direction aspre-processing for the embedded signal 923, and by performing geometricdeformation correction in the space direction for the detection complexpattern 961, spatial geometric deformation correction can be performedefficiently and accurately.

<Digital Watermark Detection Apparatus—Temporal Demodulation Unit>

In the following, details of operation of the temporal demodulation unit210 are described.

FIG. 25 shows a configuration example of the temporal demodulation unitin the first embodiment of the present invention.

The temporal demodulation unit 210 shown in the figure includes aperiodic signal generation unit 211, demodulation units 212, and acomplex pattern configuration unit 213, and it receives the embeddedsignal 923 and outputs the detection complex pattern 961.

By the way, in FIG. 25, please note that the configuration is shown suchthat information flows from the bottom to the top to facilitateunderstanding of correspondence to FIG. 18.

Demodulation processes of the embedded signal 923 by the temporaldemodulation unit 210 is performed in the following procedure.

FIG. 26 is a flowchart of operation of the temporal demodulation unit inthe first embodiment of the present invention.

Step 601) The periodic signal generation unit 211 generates two periodicsignals that have the same basic frequency and that are orthogonal. Forexample, two periodic signals may be generated based on one periodicsignal such that the phases are different with each other by 90 degrees,that is, 1/4 period. The periodic signal to be generated corresponds tothe periodic signal generation unit 131 included in the temporalmodulation unit 130 a in the before-mentioned digital watermarkembedding apparatus 100. Examples of the periodic signals are asdescribed before.

Step 602) The demodulation unit 212 performs demodulation by each of thetwo periodic signals generated in step 601 based on the time directioncomponent of the received embedded signal 923, so as to obtain twoN−1-dimensional signals. Concrete examples of demodulation are describedlater.

Step 603) The complex pattern configuration unit 213 obtains thedetection complex pattern 961 that is a N−1 dimensional pattern ofcomplex numbers in which the real part and the imaginary part become thetwo N−1-dimensional signals demodulated in the demodulation unit 212respectively.

More particularly, assuming that the two N−1-dimensional signals areQ_(r)(x₁, x₂, . . . x_(N−1)) and Q_(i)(x₁, x₂, . . . x_(N−1))respectively, and that the detection complex pattern 961 is Q(x₁, x₂, .. . x_(N−1)), it is obtained as follows, wherein j is the imaginaryunit.Q(x ₁ , x ₂ . . . x _(N−1))=Q _(r)(x ₁ , x ₂ . . . , x _(N−1))+jQ _(i)(x₁ , x ₂ , . . . , x _(N−1))  (57)

In the following, concrete examples of temporal demodulation aredescribed.

Demodulation in the demodulation units 212 is performed by obtaining thephases of the periodic signals generated by the periodic signalgeneration unit 211 of the N-dimensional embedded signal 923.Especially, by obtaining the size of components of the two periodicsignals as described below, the phases of the periodic signals can beeasily measured.

That is, more particularly, following processes are performed, forexample.

In the following, it is assumed that the N-dimensional embedded signal923 is represented as I″(x₁, x₂, . . . , x_(N−1), t).

In addition, it is assumed that two periodic signals f_(r)(t) andf_(i)(t) are generated in the periodic signal generation unit 211. Here,an example is taken in which f_(r) and f_(i) are generated based on asame periodic signal such that the phases are different by 90 degrees asfollows.f _(i)(t)=f _(r)(t−T/4)  (58)

I″ is demodulated by f_(r)(t) and f_(i)(t), so that two N−1-dimensionalsignals Q_(r)(x₁, x₂, . . . x_(N−1)) and Q_(i)(x₁, x₂, . . . , x_(N−1),t) are obtained by the following equationsQ _(r)(x ₁ , x ₂ , . . . , x _(N−1))=∫₁ ² I″(x ₁ , x ₂ , . . . , x_(N−1), τ)f _(r)(τ)dτ  (59)Q _(l)(x ₁ , x ₂ , . . . , x _(N−1))=∫₁ ² I″(x ₁ , x ₂ , . . . , x_(N−1), τ)f _(l)(τ)dτ  (60)wherein t₁ and t₂ are a start point and an end point in a section thatis a target for detection in the embedded signal 923. For example, t₁=−∞and t₂=∞ may be applied such that the whole of the received embeddedsignal 923 becomes the detection target, or t₁=0 and t₂=nT (T is aperiod of the periodic signal generated in the periodic signalgeneration unit 211) may be applied so as to extract n periods of thereceived embedded signal 923.

In addition, when the embedded signal 923 is obtained as a discretesignal, two N−1-dimensional signals Q_(r) and Q_(i) may be obtained bythe following product sum calculation.

$\begin{matrix}{{Q_{r}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1}} \right)} = {\sum\limits_{\tau = t_{1}}^{t_{2}}{{I^{''}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1},\tau} \right)}{f_{r}(\tau)}}}} & (61) \\{{Q_{i}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1}} \right)} = {\sum\limits_{\tau = t_{1}}^{t_{3}}{I^{''}\;\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1},\tau} \right){f_{i}(\tau)}}}} & (62)\end{matrix}$

In addition, for example, in a video signal and the like, when detectingdigital watermark from a re-taken video using a low-performanceprocessor such as a cellular phone and the like, there may be a case inwhich frame rate in video-taking is not stable so that timing ofsampling shifts slightly. In such a case, using the detection time t₁,t₂, . . . , t_(n) for each of the discretely obtained signals I″(x₁, x₂,. . . , x_(N−1), 1), I″(x₁, x₂, . . . , x_(N−1), 2), I″(x₁, x₂, . . . ,x_(N−1), n), product sum calculation is performed based on a product ofi-th sample and the value f(t_(i)) of the periodic function at i-thmeasurement time as follows so that unstable frame rate is corrected andaccuracy of calculation result can be maintained.

$\begin{matrix}{{Q_{r}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1}} \right)} = {\prod\limits_{i = 1}^{n}{{I^{''}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1},i} \right)}{f_{r}\left( t_{i} \right)}}}} & (63) \\{{Q_{i}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1}} \right)} = {\prod\limits_{i = 1}^{n}{{I^{''}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1},i} \right)}{f_{i}\left( t_{i} \right)}}}} & (64)\end{matrix}$

In addition, when a video displayed on a screen or a TV is taken by avideo camera or a camera of a cellular phone and the like, informationon the frame rate of reproduction and the frame rate of the video takinghave been obtained in most cases, and by obtaining t_(i) by using it,following calculation can be performed for the discretely obtainedsignals I″ (x₁, x₂, . . . , x_(N−1), 1), (x₁, x₂, . . . , x_(N−1), 2), .. . , I″(x₁, x₂, . . . , x_(N−1), n)

$\begin{matrix}{t_{i} = \frac{i}{F}} & (65) \\{{Q_{r}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1}} \right)} = {\sum\limits_{i = 1}^{n}{{I^{''}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1},i} \right)}{f_{r}\left( t_{i} \right)}}}} & (66)\end{matrix}$wherein F indicates a frame rate when taking the video.

Next, temporal demodulation using difference/differentiation isdescribed. Instead of the above-mentioned method, demodulation may beperformed using difference or differentiation of the embedded signal 923I″(x₁, x₂, . . . , x_(N−1), t) in t axis direction. A configurationexample of such temporal demodulation unit 310 is shown in FIG. 27.

The temporal demodulation unit 210 b shown in FIG. 27 has aconfiguration almost same as that of the temporal demodulation unit 210a shown in FIG. 25, and temporal demodulation unit 210 b is different inthat it is configured such that the embedded signal 923 is supplied tothe demodulation units 212 after it is supplied to the signaldifferentiation unit 215.

The signal differentiation unit 215 is configured to calculatedifference or differentiation in an axis of N-th dimension, that is, inat axis direction for the received embedded signal 923 so as to outputdifference or differentiation to the demodulation units 212.

For example, considering video signals and the like, it is known thatcorrelation between frames of the signal is large. Since the shorter thetime interval between two frames is, the higher the correlation betweenframes is, when difference or differentiation values between frames arecalculated, original image component is canceled by an amount equal toor greater than the canceled amount by the periodic signal, so thatenergy of the digital watermark relatively increases. Thus, detection ofdigital watermark becomes easy by performing demodulation from thedifference value or differentiation value, so that there is an advantagethat detection accuracy improves. Inversely, since detection performanceof similar extent can be maintained even though weaker digital watermarkis embedded, digital watermark embedding in which deterioration ofsignal is smaller becomes possible.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit>

Next, the detection information extraction unit 220 is described indetail.

FIG. 28 shows a configuration example of the detection informationextraction unit in the first embodiment of the present invention.

The detection information extraction unit 220 a includes a detectionsequence extraction unit 221, a correlation value calculation unit 222,a maximum value determination unit 223, and a detection informationreconfiguration unit 224, and receives the detection complex pattern 961from the pattern storage unit 250 and outputs detection information 914.

By the way, in FIG. 28, please note that the configuration is describedsuch that information flows from the bottom to the top to facilitateunderstanding of correspondence to FIG. 12.

Detection information extraction processes by the detection informationextraction unit 220 a are performed according to the followingprocedure.

FIG. 29 is a flowchart of operation of the detection informationextraction unit in the first embodiment of the present invention.

Step 701) The detection sequence extraction unit 221 configures adetection sequence 1113 by extracting values of the real part and theimaginary part from complex number values obtained from the receiveddetection complex pattern 961 and arranging the values. Details of thedetection sequence extraction unit 221 are described later.

Step 702) The correlation value calculation unit 222 calculatescorrelation between the detection sequence 1113 configured by thedetection sequence extraction unit 221 and an embedding sequenceconfigured based on an assumed embedding sequence to obtain acorrelation value 1114.

When different values are embedded according to the kind of theembedding sequence, correlations are calculated for each of a pluralityof embedding sequences configured based on a plurality of conceivableembedding sequences so as to obtain corresponding correlation values1114.

Details of the operation of the correlation value calculation unit 222are described later.

Step 703) The maximum value determination unit 223 finds maximum one ofcorrelation values 1114 obtained by the correlation value calculationunit 222 so as to determine an embedding sequence used for correlationcalculation in the correlation value calculation unit 222 correspondingto the maximum correlation value 1114.

By the way, depending on the configuration method of the embeddingsequence in the digital watermark embedding apparatus 100, thedetermination may be performed by other methods instead of determiningthe maximum value by the maximum value determination unit 223.

Details of operation of the maximum value determination unit 223, anddetails of other alternative methods are described later.

Step 704) The detection information reconfiguration unit 224reconfigures detection information that is determined to be actuallyembedded based on the embedding sequence determined by the maximum valuedetermination unit 223. By the way, details of operation of thedetection information reconfiguration unit 224 are described later.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—Detection Sequence Extraction Unit>

Next, details of the detection sequence extraction unit 221 aredescribed.

The detection sequence extraction unit 221 is responsible for afunction, in the detection side, corresponding to the complex arraygeneration unit 112 in the complex pattern generation unit 110 a of thedigital watermark embedding apparatus 100, and configures the detectionsequence 1113 from the complex number values obtained from the detectioncomplex pattern 961.

Processes in the detection sequence extraction unit 221 are executedaccording to the following procedure.

FIG. 30 is a flowchart of detailed operation of the detection sequenceextraction unit in the first embodiment of the present invention.

Step 801) The detection sequence extraction unit 221 configuresN−1-dimensional complex array of a size of M₁×M₂× . . . ×M_(N−1), andstores it in a memory (not shown in the figure). M₁, M₂, . . . , M_(N−1)are element numbers similar to those used in the complex arraygeneration unit 112 of the digital watermark embedding apparatus 100.

When the detection complex pattern 961 is obtained as a discrete signal,it is regarded as the N−1-dimensional complex array as it is. When thedetection complex pattern 961 is obtained as a continuous signal, dataobtained by sampling the detection complex pattern 961 using arbitrarysampling means is used as the N−1-dimensional complex array.

Step 802) Complex number values are extracted one by one in sequencefrom the complex array obtained in step 801 from the memory (not shownin the figure), so that the real part and the imaginary part of theextracted complex number value are regarded as independent real valuesand arranged. That is, assuming that the complex array is represented asA[p₁, p₂, . . . , p₁, p₂, . . . p_(N−1)] (p_(n)≧0) and that thedetection sequence 1114 is represented as i″₁, i″₂, . . . , i″_(L),

$\begin{matrix}{{i_{1}^{''} = {\left\lbrack {A\left\lbrack {0,0,\ldots\mspace{14mu},0} \right\rbrack} \right\rbrack}}{i_{2}^{''} = {{??}\left\lbrack {A\left\lbrack {0,0,\ldots\mspace{14mu},0} \right\rbrack} \right\rbrack}}{i_{3}^{''} = {\left\lbrack {A\left\lbrack {1,0,\ldots\mspace{14mu},0} \right\rbrack} \right\rbrack}}{i_{4}^{''} = {{??}\left\lbrack {A\left\lbrack {1,0,\ldots\mspace{14mu},0} \right\rbrack} \right\rbrack}}} & (68)\end{matrix}$wherein,

, ℑ

indicates calculation for extracting each of the real part and theimaginary part of the complex number.

This process is a symmetric process with respect to generation processin the complex array generation unit 112 of the digital watermarkembedding apparatus 100.

Step 803) The obtained i″₁, i″₂, . . . , i″_(L) are output as thedetection sequence 1113. In addition, in the case when the order of theembedding sequence 913 is permuted to random order using pseudo-randomnumbers for embedding before the complex array is configured in thecomplex array generation unit 112 of the digital watermark embeddingapparatus 100, the order of the detection sequence 1113 is permutedinversely with respect to the process by the complex array generationunit 112 using the pseudo-random number before step 803, so that theorder is restored to an order that can be associated with the embeddingsequence 913. In this case, as a value of the seed of the pseudo-randomnumber used for permuting the order, a key same as one used when digitalwatermark embedding is provided as a key for digital watermarkdetection.

When the complex array generation unit 112 of the digital watermarkembedding apparatus 100 performs order permutation by permuting elementsof the obtained complex array instead of permuting the embeddingsequence 913, the order may be restored by permuting the order ofelements of the complex array configured in step 801 inversely withrespect to the process in the complex array generation unit 112 beforethe step 802.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—Correlation Value Calculation Unit>

Next, detailed operation of the correlation value calculation unit 222of the detection information extraction unit 220 a is described.

Correlation value calculation processes in the correlation valuecalculation unit 222 are performed according to the following procedure.

1) The correlation value calculation unit 222 generates conceivableembedding sequences w⁽¹⁾, w⁽²⁾, . . . by a procedure similar to that inthe embedding sequence generation unit 111 of the digital watermarkembedding apparatus 100.

The conceivable embedding sequences are all embedding sequences that maybe embedded, and they can be determined according to generation of theembedding sequence in the embedding sequence generation unit 111 asfollows, for example.

EXAMPLE 1

For example, when the embedding sequence has been generated according to(example 1) of the embedding sequence generation unit 111, theconceivable embedding sequence is one, and that is as follows.w=PN={PN₁, PN₂, . . . , PN_(L)}  (69)

EXAMPLE 2

For example, when the embedding sequence has been generated according to(example 2) of the embedding sequence generation unit 111, theconceivable embedding sequences are two, and those are as follows.w⁽¹⁾=PN={PN₁, PN₂, . . . , PN_(L)}  (70)w ⁽²⁾ =−PN={−PN ₁ , −PN ₂ , . . . , PN _(L)}  (71)

EXAMPLE 3

For example, when embedding sequence has been generated like the examplein which each symbol represents one bit information in (example 3) inthe embedding sequence generation unit 111, the conceivable sequencesare two, and those are as follows.w^((i, 1))=PN_(i)={pn_(i1), pn_(i2), . . . , pn_(iL)}  (72)w^((i, 2))=−PNi={−pn_(i1),−pn_(i2), . . . , −pn_(iL)}  (73)

In addition, in (example 3) of the embedding sequence generation unit111, when the embedding sequence has been generated like the example inwhich each symbol represents 12 bits information, there are 4096conceivable sequences as follows for each symbol i.

$\begin{matrix}{{w^{({i,1})} = {PN}_{({i,0})}}{w^{({i,2})} = {PN}_{({i,1})}}\vdots{w^{({i,4096})} = {PN}_{({i,4095})}}} & (74)\end{matrix}$

EXAMPLE 4

For example, when the embedding sequence has been generated like anexample in (example 4) of the embedding sequence generation unit 111,there are 2^(n) embedding sequences that can by considered to simplycover all cases. In later correlation calculation, the detectionsequence 1113 may be divided into groups of m, so that correlationbetween the following two kinds of embedding sequences and the divideddetection sequence 1113 may be calculated for each one bit b_(i).w ^((i,1)={+PN) _(im+1) ,+PN _(im+2) , . . . ,+PN _(im+m)}  (75)w ^((i,2)) ={−PN _(im+1) ,+PN _(im+2) , . . . ,−PN _(im+m)}  (76)Such a method is also described in Takao Nakamura, Atsushi Katayama,Masashi Yamamuro, Noboru Sonehara, “Fast Watermark Detection Scheme fromAnalog Image for Camera-equipped Cellular Phone”, IEICE TransactionsD-II, Vol. j87-D-II, No. 12, pp. 2145-2155, 2004.

2) Correlation is calculated between the detection sequence 1113obtained by the detection sequence extraction unit 221 and each of theembedding sequences obtained in the above-mentioned 1).

Correlation calculation is similar to one performed in digital watermarkdetection shown in patenet document 1, and the document—Takao Nakamura,Hiroshi Ogawa, Atsuki Tomioka, Youichi Takashima, “An Improvement ofWatermark Robustness against. Moving and/or cropping the area of theImage”, The 1999 Symposium on Cryptography and Information Security,SCIS99—W3-2.1, pp. 193-198, 1999—, for example, and correlation can beobtained by the following product sum calculation, wherein ρ^((j)) is acorrelation value to be obtained, i″={i″₁, i″₂, . . . , i″_(L)} is thedetection sequence 1113, w^((j))={w^((j)) ₁, w^((j)) ₂, . . . , w^((j))_(L)} is the embedding sequence that is a current process, and “·” isproduct sum operation in which a number sequence is regarded as avector.

$\begin{matrix}{\rho^{(j)} = {{i^{''} \cdot w^{(j)}} = {\sum\limits_{k = 1}^{L}{i_{k}^{''}w_{k}^{(j)}}}}} & (77)\end{matrix}$For aligning evaluation criteria of detection reliability as describedin the before-mentioned document—Takao Nakamura, Atsushi Katayama,Masashi Yamamuro, Noboru Sonehara, “Fast Watermark Detection Scheme fromAnalog Image for Camera-equipped Cellular Phone”, IEICE TransactionsD-II, Vol. j87-D-II, No. 12, pp. 2145-2155, 2004—, each element of i″and w^((j)) may be normalized beforehand such that the average becomes 0and that the variance becomes 1 so that calculation may be performed bymultiplying by a constant term in the correlation value calculation asfollows.

$\begin{matrix}{\rho^{(j)} = {{\frac{1}{\sqrt{L}}{i^{''} \cdot w^{(j)}}} = {\frac{1}{\sqrt{L}}{\sum\limits_{k = 1}^{L}{i_{k}^{''}w_{k}^{(j)}}}}}} & (78)\end{matrix}$

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—Maximum Value Determination Unit>

Next, the maximum value determination unit 223 of the detectioninformation extraction unit 220 a is described in detail.

Processes in the maximum value determination unit 223 is performedaccording to the following procedure.

1) The maximum value determination unit 223 finds a maximum correlationvalue ρ^((j)) from the correlation values 1114 ρ⁽¹⁾, ρ⁽²⁾, . . .obtained by the correlation value calculation unit 222 as follows,ρ^((max))=MAX(ρ⁽¹⁾, ρ⁽²⁾, . . . )  (79)wherein MAX( ) is an operation for returning a maximum value.

2) An embedding sequence w^((max)) corresponding to ρ^((max)) isobtained.

In addition, the maximum value determination unit 223 may determinewhether the maximum correlation value ρ^((max)) exceeds a predeterminedthreshold to determine that digital watermark is not embedded when thevalue does not exceed the predetermined threshold.

In the following, alternative operation of the maximum valuedetermination unit 223 is described.

Instead of maximum value determination by the maximum valuedetermination unit 223, the correlation value calculation unit 222 doesnot calculate correlation for all of the embedding sequences w⁽¹⁾.),w⁽²⁾, . . . , but calculates correlation from the embedding sequencew⁽¹⁾ sequentially, performs determination based on whether the obtainedcorrelation value exceeds a predetermined threshold, and determines anembedding sequence by which the correlation value exceeds the thresholdas w^((max)) so that the correlation value calculation unit 222 may endcorrelation calculation at that time.

In addition, when the embedding sequence in the digital embeddingapparatus 100 is embedded being configured only by one kind of embeddingsequence like one shown in (example 1) of the embedding sequencegeneration unit 111, maximum value determination by the maximum valuedetermination unit 223 has no meaning since only one correlation valueis calculated. Instead, determination may be performed based on whetherthe obtained correlation value exceeds the predetermined threshold.

In addition, when the embedding sequence in the digital watermarkembedding apparatus 100 is embedded by being configured based ondifference of plus and minus of one kind of embedding sequence like oneshown in (example 23) of the embedding sequence generation unit 111,since correlation values of inverted signs are obtained, the correlationcalculation in the correlation value calculation unit 222 may beperformed only on one embedding sequence, and embedded value may bedetermined based on the sign of the obtained correlation value insteadof the maximum value determination by the maximum value determinationunit 223. In addition, determination may be performed based on whetherthe absolute value of the obtained correlation value exceeds thepredetermined threshold.

In addition, reliability of watermark detection may be evaluated by thesize of the correlation value.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—Detection Information Reconfiguration Unit>

Next, the detection information reconfiguration unit 224 of thedetection information extraction unit 220 a is described in detail.

Processes in the detection information reconfiguration unit 223 areperformed according to the following procedure.

1) According to the embedding sequence generation method in theembedding sequence generation unit 111 of the digital watermarkembedding apparatus 100, values of corresponding embedding informationare configured as detection information from the embedding sequencew^((max)) obtained by the maximum value determination unit 223. Forexample, when the embedding sequence is configured by spectrumspreading, the detection information is reconfigured such that w^((max))is spectrum despread.

EXAMPLE 1

For example, when the embedding sequence has been generated like(example 1) of the embedding sequence generation unit 111, informationindicating whether digital watermark is embedded becomes detectioninformation.

EXAMPLE 2

For example, when the embedding sequence has been generated like(example 2) of the embedding sequence generation unit 111, whenw^((max))=PN, detection information becomes bit value 1, and whenw^((max))=−PN, detection information becomes bit value 0.

EXAMPLE 3

For example, when the embedding sequence has been generated like theexample in which each symbol represents information of one bit in the(example 3) of the embedding sequence generation unit 111, whenw^((max))=PN_(i) for symbol i, the symbol value is 1, and whenw^((max))=−PN_(i), the symbol value becomes 0. This is performed forevery symbol so that detection information is obtained by connecting theobtained symbol values.

When the embedding sequence has been generated like the example in whicheach symbol represents information of 12 bits in the (example 3) of theembedding sequence generation unit 111, when w^((max))=−PN_((i, x)) forsymbol i, the symbol value is x. This is performed for every symbol sothat detection information is obtained by connecting the obtained symbolvalues.

EXAMPLE 4

For example, when the embedding sequence has been generated like anexample in (example 4) of the embedding sequence generation unit 111,when w^((max))={+PN_(im+1), +PN_(im+2), . . . , +PN_(im+m)} for bit thebit value becomes +1, and when w^((max))={−PN_(im+1), −PN_(im+2), . . ., −PN_(im+m)}, the bit value becomes −1. This is performed for every bitand detection information 914 is obtained by connecting the obtained bitvalues.

2) The detection information 914 obtained in the above-mentioned way isoutput.

<Other Method for Embedding into Complex Number>

Next, other method for embedding into complex number is described.

In the above-mentioned configuration examples, in the complex arraygeneration unit 112 of the digital watermark embedding apparatus 100,element values of complex array is set from the embedding sequence 913such that values extracted from the embedding sequence 913 becomes thereal part and the imaginary part of the element values. In addition,corresponding to that, when the detection sequence extraction unit 221of the digital watermark detection apparatus 200 configures thedetection sequence 1113 from the detection complex pattern 961, thedetection sequence 1113 is configured by extracting the real part andthe imaginary part of the complex number values of the detection complexpattern 961 and by arranging them.

In these examples, although the real part and the imaginary part of thecomplex number are used, the complex number values may be used indifferent ways as long as operations of the complex array generationunit 112 and the detection sequence extraction unit 221 are associatedwith each other.

For example, assuming that values extracted from the embedding sequence913 in the complex array generation unit 112 are w_(l) and w₂, these maybe set to be argument and absolute value of the element value of thecomplex array. In this case, the detection sequence extraction unit 221may configure the detection sequence 1113 using the argument and theabsolute value of the complex number value of the detection complexpattern 961.

In addition, for example, one value w₁ extracted from the embeddingsequence 913 may be embedded by associating it with an argument of acomplex number value. In this case, the absolute value of the complexnumber value may be fixed to 1, for example. For example, when the valueof the embedding sequence takes either one of +1 and −1, arguments ofthe complex number value may be set to be π/4 and 3π/4, respectively. Inthis case, the detection sequence extraction unit 221 may configure thedetection sequence 1113 using only the argument of the complex numbervalue of the detection complex pattern 961. In the case when adopting aconfiguration method like this, instead of calculating the complex arrayas an array of complex numbers, it may be configured as an array of realnumbers representing the values of argument, so that the temporalmodulation unit 130 may be configured so as to control the phase of theperiodic variable using the values. When such a configuration method isadopted, the length of the embedding sequence becomes half compared withthe case when values are set to the real part and the imaginary part ofcomplex number.

In addition, for example, an element value p of a complex array may bedetermined for w₁ and w₂ by the following equation,p=aw ₁ +bw ₂  (79)wherein a and b are arbitrary complex numbers satisfying the followingequation.ℑ[a*b]≠0

The a and b may be determined to be complex numbers that are orthogonalon the complex plane, that is, they may be determined so as to satisfythe following equation.

[c1*c2]=0In the equation, * indicates complex conjugate, and

[ ], ℑ[ ]indicates operation for extracting the real part and the imaginary partof the complex number respectively.

In this case, in the detection sequence extraction unit 221, values i″₁and i″₂ of the detection sequence 1113 can be obtained from the complexnumber q of the detection complex pattern 961 using an inverse transformof the above-mentioned transform.

In addition, for example, points on the complex plane (for example, fourpoints of {±√{square root over (1/2)}±j√{square root over (1/2)}}) maybe selected like QAM modulation according to the value of one value w₁extracted from the embedding sequence 913, so that complex number valuesof the selected points may be used.

Characteristics of First Embodiment

The above-mentioned present embodiment include followingcharacteristics.

Deletion of noise component) According to the digital watermarkembedding apparatus 100 and the digital watermark detection apparatus200 of the present embodiment, for digital watermark that is embedded bybeing modulated by the periodic signal in the temporal modulation unit130 in digital watermark embedding, detection is performed by performingintegral calculation with the periodic signal in the temporaldemodulation unit 210 in digital watermark detection. By doing that,variance of the before-embedding signal 912 that becomes noise fordigital watermark and noise component applied after that becomes small(this is because the periodic signal is determined such that a valueobtained by calculating integral of the periodic signal for one periodbecomes 0). Especially, as to video signals, it is known thatcorrelation between adjacent frames is relatively high. By the integralcalculation with the periodic signal, components in which correlation inthe time direction is high within the period are removed. As a result,variance due to the before-embedding signal 912 becomes dramaticallysmall.

According to the before-mentioned document: Susumu Yamamoto, TakaoNakamura, Youichi Takashima, Atsushi Katayama, Ryo Kitahara, TakashiMiyatake, “Consideration on evaluation of detectability for frame-basedvideo watermarking”, Forum on information technology, FIT2005, J-029,2005, in the case of digital watermark using spectrum spreading andcorrelation calculation, the smaller the variance of thebefore-embedding signal is, the larger the detection evaluation valueindicating reliability of detection in the sense of false positive ofdigital watermark is. (In the above-equations (3) and (4), the smallerσ²n_(i)included in B and C of the denominator is, the larger the expected valueE[ρ] of the detection evaluation value becomes). This means that thesmaller the variance of noise component included in i″ is in thecorrelation calculation in the correlation value calculation unit 222,the higher the reliability for detection becomes, and it means thatreliability for detection is high in the digital watermark embeddingapparatus and the digital watermark detection apparatus in the presentinvention.

By generating the N−1-dimensional embedding complex pattern 921 as thecomplex number array based on the embedding sequence 913 that isgenerated by using the pseudo-random number and modulating theN−1-dimensional embedding complex pattern 921 by the periodic signals inwhich phases are different by 90 degrees, the phase of the embeddingpattern 922 is spread in the N−1 dimensional space, so that the size ofthe noise component that appears due to the before-embedding signal 912when detecting digital watermark becomes small. As a result, morereliable digital watermark embedding and detection become possible, anddigital watermark embedding and detection with smaller qualitydeterioration become possible by maintaining reliability similar toconventional techniques.

Increase of spectrum spread sequence length) In addition, by embeddingdigital watermark embedding sequence as a N−1-dimensional pattern ofcomplex numbers, spectrum spread sequence two times longer can be usedcompared with the digital watermark method, in which digital watermarkfor still images is embedded to each frame repeatedly, like the methoddisclosed in the before-mentioned document: Takao Nakamura, HiroshiOgawa, Atsuki Tomioka, Youichi Takashima, “An Improvement of WatermarkRobustness against. Moving and/or cropping the area of the Image”, The1999 Symposium on Cryptography and Information Security, SCIS99—W3-2.1,pp. 193-198, 1999.

According to the before-mentioned document: Susumu Yamamoto, TakaoNakamura, Touichi Takashima, Atsushi Katayama, Ryo Kitahara, TakashiMiyatake, “Consideration on evaluation of detectability for frame-basedvideo watermarking”, Forum on information technology, FIT2005, J-029,2005, as to digital watermark using spectrum spreading and correlationcalculation, the detection evaluation value indicating reliability ofdetection in the sense of false positive of digital watermark increasesin proportion to the square root of the sequence length of the spectrumspreading (in the equations (3) and (4) in the document, E[ρ] is inproportion to the numerator √1). This means that, as the spectrum spreadsequence increase, highly reliable detection becomes possible by theincrease. Thus, compared with conventional schemes, √2 times largerdetection evaluation value can be obtained by the digital watermarkembedding apparatus and the digital watermark detection apparatus of thepresent invention, so that it represents that reliability of detectionis high.

In addition, in the case when reliability of detection of similar degreeof the conventional schemes is necessary, instead of doubling thespectrum spread sequence length, by embedding separate information toeach, the embedding information length can be doubled as a whole.

Modulation in the N dimensional direction) The temporal modulation unit130 modulates the N−1-dimensional embedding pattern, on which spectrumspreading has been performed in the N−1-dimensional space, using theperiodic signals in the N-th dimension direction that is orthogonal tothe N−1-dimensional embedding pattern, so that it has characteristicsthat desynchronization applied in the N-th dimension direction exertscommon influence in the N−1-dimensional space.

In addition, because of redundancy obtained by spreading embeddinginformation of the N−1-dimensional pattern into the N-dimensional space,there is sufficient tolerance for modification such as high compressionand re-taking in the case of video signal, for example, and also when apart of a signal (a part of frames in the case of video signal, forexample) is modified, or also when a part of a signal is cropped (in thecase of video signal, when a part of a frame section is cut apart, forexample), detection of digital watermark becomes possible, and also inthese cases, detection of digital watermark can be performed forinformation of long information length while suppressing qualitydeterioration.

Prevention of occurrence of weak frame) In addition, the temporalmodulation unit 130 uses, as the embedding pattern, a sum of signalsmodulated using two periodic signals that are orthogonal or havedifferent phases. If modulation is performed using only one periodicsignal, in the case of embedding to the video signal, for example, thereis a possibility in that every value of the embedding pattern becomesless that a minimum video signal quantization value so that a frame towhich digital watermark embedding is not performed actually occurs. Inaddition, while such a frame is left unchanged, attack for deletingdigital watermark becomes possible by changing a frame in whichamplitude of watermark component is large so that watermark issufficiently embedded. By using, as the embedding pattern, the sum ofsignals modulated by the two periodic signals that are orthogonal orhave different phases like the digital watermark embedding apparatus inthe preset embodiment, it can be prevented to produce a frame in whichdigital watermark becomes less than the minimum video signalquantization value so that digital watermark embedding is not performedactually. Thus, the video signal as a transmission route of digitalwatermark can be used effectively and robustness can be increased forthe attack for aiming and changing a frame in which amplitude of digitalwatermark is large.

Effects of detection from difference/differentiation) In addition, byusing the configuration of FIG. 27 as the temporal demodulation unit210, since demodulation is performed from the difference value or thedifferentiation value, original image component is canceled by an amountequal to or greater than that canceled by the periodic signals, so thatdetection of digital watermark becomes easy and detection accuracyimproves. Inversely, since detection performance of similar extent canbe maintained even though weaker digital watermark is embedded, digitalwatermark embedding in which deterioration of signal is smaller isavailable.

Solving of the problem of synchronization) In addition, although notused in the digital watermark detection apparatus of the presentembodiment, by using digital watermark detection apparatuses describedin the after-mentioned fourth embodiment and the fifth embodiment, thedigital watermark embedding apparatus of the present embodiment hascharacteristics that digital watermark that does not requiresynchronization or that makes it possible to perform synchronizationeasily and rapidly can be embedded using the fact that an embeddingsequence to which spectrum spreading has been performed in theN−1-dimensional space receives common influence of desynchronization inthe N-th dimension direction.

Robustness to time direction scheduling) In addition, in the digitalwatermark embedding apparatus in the present embodiment, by using arelatively low frequency as a frequency of the periodic signal used inthe temporal modulation unit 130, digital watermark detection can beperformed with robustness to some extent for attack including expansionand contraction in the time direction such as frame rate conversion,frame drop and frame insertion.

Effects as a whole) In addition, since reliability is high androbustness is increased in digital watermark detection as a whole, lessstrength is required in digital watermark embedding for obtainingdetection reliability and robustness of similar degree of conventionaltechniques. Thus, quality deterioration of a signal due to digitalwatermark can be made smaller, so that, when performing embedding into avideo signal, for example, image quality of the digital watermarkembedded video can be made high.

[Second Embodiment]

<One Dimensional FFT Temporal Modulation>

In the following, a digital watermark embedding apparatus and a digitalwatermark detection apparatus in the second embodiment are described.

The digital watermark embedding apparatus and the digital watermarkdetection apparatus in the present embodiment are examples in whichtemporal modulation and demodulation processes in the digital watermarkembedding apparatus and the digital watermark detection apparatus of thefirst embodiment are realized by one dimensional Fourier transformprocesses.

The digital watermark embedding apparatus of the present embodiment hasa configuration similar to that of the digital watermark embeddingapparatus 100 of the first embodiment, and only the temporal modulationunit 130 has a different configuration.

The digital watermark detection apparatus of the present embodiment hasa configuration similar to that of the digital watermark detectionapparatus 200 of the first embodiment, and only the temporaldemodulation unit 210 has a different configuration.

<Digital Watermark Embedding Apparatus—Temporal Modulation Unit>

FIG. 31 shows a configuration example of the temporal modulation unit inthe digital watermark embedding apparatus of the second embodiment. Thetemporal modulation unit 130 b shown in the figure includes onedimensional inverse Fourier transform unit 134. The one-dimensionalinverse Fourier transform unit 134 receives an embedding complex pattern921 and outputs an embedding pattern 922.

Generation processes of the embedding pattern 922 by the temporalmodulation unit 130 b are performed in the one-dimensional inverseFourier transform unit 134 according to the following procedure.

FIG. 32 is a flowchart showing operation of the temporal modulation unitin the second embodiment of the present invention.

Step 901) P(x₁, x₂, . . . , x_(N−1)) for the position (x₁, x₂, . . . ,x_(N−1)) of the embedding complex pattern 921 is regarded as a Fouriercoefficient for a particular frequency in an N-th dimension axis (timeaxis, for example).

Step 902) Discrete inverse Fourier transform is performed on the Fouriercoefficient of step 901 with respect to the N-th dimension axis so as toobtain one-dimensional sequence for the position (x₁, x₂, . . . ,x_(N−1)).

Step 903) An N-dimensional pattern including the one-dimensionalsequence of step 902 as a value of each position is regarded as theembedding pattern 922.

In the following, these are described more particularly using equations.

Assuming that the embedding complex pattern 921 is P(x₁, x₂, . . . ,x_(N−1)). A discrete Fourier coefficient pattern ξ(x₁, x₂, . . . ,x_(N−1), u) is configured using P(x₁, x₂, . . . , x_(N−1)) as follows,

$\begin{matrix}{{\xi\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1},u} \right)} = \left\{ \begin{matrix}{P\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1}} \right)} & \left( {u = u_{0}} \right) \\{P^{*}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1}} \right)} & \left( {u = {U - u_{0}}}\; \right) \\0 & \left( {{u \neq u_{0}},{U - u_{0}}} \right)\end{matrix} \right.} & (81)\end{matrix}$wherein * indicates complex conjugate, u₀ indicates a predeterminedfrequency, and U indicates a number of frequency samples. The reason forproviding the conjugate complex number of P by u=u₀ and u=U−u₀ is thatthe signal obtained by performing discrete inverse Fourier transformbecomes a real number value.

One-dimensional discrete inverse Fourier transform is performed on ξwith respect to u so as to obtain the embedding pattern W(x₁, x₂, . . ., x_(N−1), t).

<Digital Watermark Detection Apparatus—Temporal Demodulation Unit>

Next, the temporal demodulation unit 210 of the digital watermarkdetection apparatus 200 in the second embodiment is described.

FIG. 33 shows a configuration example of the temporal demodulation unitin the second embodiment of the present invention.

The temporal demodulation unit 210 c of FIG. 33 includes aone-dimensional Fourier transform unit 214, receives the embedded signal923, and outputs the detection complex pattern 961.

By the way, in FIG. 33, please note that the configuration is shown suchthat information flows from the bottom to the top to facilitateunderstanding of correspondence to FIG. 31.

Demodulation processes for the embedded signal 923 by the temporaldemodulation unit 210 c are performed according to the followingprocedure.

FIG. 34 is a flowchart of operation of the temporal demodulation unit inthe second embodiment of the present invention.

Step 1001) A predetermined section T is extracted from the receivedembedded signal 923.

Step 1002) One-dimensional discrete Fourier transform is performed onthe section T of step 1001 for each position (x₁, x₂, . . . , x_(N−1))to perform frequency decomposition.

Step 1003) Fourier coefficients of a predetermined frequency areextracted from the result of step 1002 to obtain the detection complexpattern 961.

These are concretely described in the following using equations.

Assuming that embedded signal 923 is I″(x₁, x₂, . . . , x₁, x_(N−1), t).One-dimensional discrete Fourier transform is performed on I″(x₁, x₂, .. . , x_(N−1), t) as follows to obtain η(x₁, x₂, . . . , x₁, x_(N−1),u),

$\begin{matrix}{{\eta\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1},u} \right)} = {\frac{1}{\sqrt{T}}{\sum\limits_{t = 0}^{T - 1}{{I^{''}\left( {x_{1},x_{2},\ldots\mspace{11mu},x_{N - 1},t} \right)}{\mathbb{e}}^{{- J}\;\frac{2\pi}{T}{ut}}}}}} & (82)\end{matrix}$wherein T is a predetermined number of samples. Assuming that thedetection complex pattern 961 is represented as Q(x₁, x₂, . . . ,x_(N−1)) so that Q(x₁, x₂, . . . , x_(N−1)) is obtained from η(x₁, x₂, .. . , x_(N−1), u) as follows,Q(x ₁ ,x ₂ . . . ,x _(N−1))=η(x ₁ ,x ₂ , . . . , x _(N−1) ,u ₀  (83)wherein, u₀ indicates a predetermined frequency.

In the following, temporal demodulation using difference/differentiationis described.

Similar to those shown in the first embodiment, instead of theabove-mentioned processes, demodulation may be performed by performingone dimensional discrete Fourier transform on the difference ordifferentiation in the t axis direction of the embedded signal 923I″(x₁, x₂, . . . , x_(N−1), t). That is, when using the difference, forexample,J 0(x ₁ , x ₂ , . . . , x _(N−1) , t)=I″(x ₁ , x ₂, . . . , x_(N−1) ,t+Δt)−I″(x ₁ , x ₂ , . . . , x _(N−1) , t)  (84)

$\begin{matrix}{{\eta\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1},u} \right)} = {\frac{1}{\sqrt{T}}{\overset{T - 1}{\sum\limits_{t = 0}}{{I^{''}\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1},t} \right)}{\mathbb{e}}^{{- J}\;\frac{2\pi}{T}{ut}}}}}} & (85)\end{matrix}$wherein it is assumed that T is a predetermined number of samples. Inaddition, Δt is a predetermined interval of samples. For example, whenΔt=1, it indicates to calculate the difference at intervals of onesample, and when a video signal is taken as an example, it indicatescalculating a difference between adjacent frames. Δt may be a numberother than 1.

A configuration example of the temporal demodulation unit 210 is shownin FIG. 35.

The temporal demodulation unit 210 d of FIG. 35 has a configurationalmost similar to that of the temporal demodulation unit 210 c of FIG.33, and it is different in that it is configured such that the embeddedsignal 923 is supplied to the one-dimensional Fourier transform unit 216after once being supplied to the signal differentiation unit 215.

The signal differentiation unit 215 calculates difference ordifferentiation for the received embedded signal 923 in the N-thdimension axis direction, that is, in the t axis direction, and outputsthe difference or the differentiation to the one-dimensional Fouriertransform unit 216.

The effect of performing demodulation by performing one-dimensionaldiscrete Fourier transform on the difference or the differentiation ofthe embedded signal 923 I″(x₁, x₂, . . . , x_(N−1), t) in the t axisdirection is the same as the effect of the temporal demodulation unit210 b shown in FIG. 27 in the first embodiment.

<Characteristics of the Second Embodiment>

Characteristics of the present invention are described.

The digital watermark embedding apparatus and the digital watermarkdetection apparatus of the present embodiment are examples in which thedigital watermark embedding apparatus and the digital watermarkdetection apparatus of the first embodiment are realized usingone-dimensional Fourier transform.

By using the one-dimensional Fourier transform, the digital watermarkembedding apparatus and the digital watermark detection apparatus can beeasily configured using an existing Fourier transform apparatus.

By the way, the digital watermark embedding apparatuses and the digitalwatermark detection apparatuses of the first embodiment and the presentembodiment may be used by combining them. That is, the temporalmodulation unit 130 b of the digital watermark embedding apparatus maybe replaced with the temporal modulation unit 130 a of the firstembodiment, and the temporal demodulation unit 210 c of the digitalwatermark detection apparatus may be replaced with the temporaldemodulation unit 210 d of the present embodiment, so that they may beused by combining them, and the temporal modulation unit 130 a of thedigital watermark embedding apparatus may be replaced with the temporalmodulation unit 130 b of the present embodiment, and the temporaldemodulation unit 210 c of the digital watermark detection apparatus maybe replaced with the temporal demodulation unit 210 d of the presentembodiment.

[Third Embodiment]

<Two-dimensional FFT Coefficient Embedding>

In the following, a digital watermark embedding apparatus and a digitalwatermark detection apparatus in the third embodiment are described.

The present embodiment is an example in which digital watermarkembedding is performed in orthogonal transform region in the digitalwatermark embedding apparatus and the digital watermark detectionapparatus of the first embodiment.

The digital watermark embedding apparatus of the present embodiment hasa configuration similar to that of the digital watermark embeddingapparatus of the first embodiment, but only the complex patterngeneration unit is different.

The digital watermark detection apparatus of the present embodiment hasa configuration similar to that of the digital watermark detectionapparatus of the first embodiment, but only the detection informationextraction unit is different.

<Digital Watermark Embedding Apparatus—Complex Pattern Generation Unit>

In the following, the complex pattern generation unit in the presentembodiment is described.

FIG. 36 shows the complex pattern generation unit of the thirdembodiment of the present invention.

The complex pattern generation unit 110 b shown in the figure includesan embedding sequence generation unit 111, a complex array generationunit 112, and an N−1-dimensional inverse Fourier transform unit 113, andhas a configuration obtained by adding the N−1-dimensional inverseFourier transform unit 113 to the configuration shown in FIG. 12. Thecomplex pattern generation unit 110 b receives the embedding information911 and outputs embedding complex pattern 921.

Processes for generating the embedding complex pattern by the complexpattern generation unit 110 b are performed according to the followingprocedure.

FIG. 37 is a flowchart of operation of the complex pattern generationunit in the third embodiment of the present invention.

Step 1101) The embedding sequence generation unit 111 generates theembedding sequence 913 that is a sequence of number values indicatingembedding information based on the received embedding information 911.Operation of the embedding sequence generation unit 111 is the same asthat in the first embodiment.

Step 1102) The complex array generation unit 112 assigns the embeddingsequence 913 generated in the embedding sequence generation unit 112 tothe real part and the imaginary part of the elements of theN−1-dimensional complex array to generate an intermediate complexpattern 904.

Operation of the complex array generation unit 112 is described later.

Step 1103) The N−1 dimensional inverse Fourier transform unit 113performs N−1-dimensional inverse Fourier transform on the intermediatecomplex pattern 904 generated in the complex array generation unit 112to generate the N−1-dimensional embedding complex pattern 921 similarly.Details of operation of the N−1-dimensional inverse Fourier transformunit 113 are described later.

<Digital Watermark Embedding Apparatus—Complex Pattern GenerationUnit—Complex Array Generation Unit>

Next, operation of the complex array generation unit 112 of the step1102 is described in detail.

Although operation of the complex array generation unit 112 may be onesame as that of the complex array generation unit of the firstembodiment, following processes may be also adopted for more effectivedigital watermark embedding.

1) An N−1-dimensional complex array of a size of M₁×M₂× . . . ×M_(N−1)in which every element value is 0 is prepared, wherein M₁, M₂, . . . ,M_(N−1) are predetermined number of elements.

2) A range of elements to which the embedding sequence 913 is assignedin the complex array is determined. An example of the range is describedlater.

3) Values are extracted from the embedding sequence 913 two by two insequence, then, values are set in the array such that the valuesextracted in sequence becomes the real part and the imaginary part ofthe element value for elements in the range determined in 2) in thearray of the 1).

4) The complex array generated in 3) is output to the N−1-dimensionalinverse Fourier transform unit 113 as the intermediate complex pattern904.

Like the complex array generation unit in the first embodiment, it isneedless to say that the order of the embedding sequence 913 may bepermuted to random order using a pseudo-random number before 3).

Such processes for generating complex array are similar to generation ofthe watermark coefficient matrix shown in the patent document 1.However, in the present invention, although the intermediate complexpattern 904 is inverse Fourier transformed by the N−1-dimensionalinverse Fourier transform unit 113 later, it is not necessary that theresult of the inverse Fourier transform becomes a real number value, andit may be a complex number. Thus, it is not necessary that theintermediate complex pattern 904 maintains symmetrical property of theFourier transform coefficients. That is, embedding of the embeddingsequence 913 can be performed using all elements in the range of 2), andit represents that two times longer embedding sequence 913 can beembedded compared with the patent document 1.

The range of the elements in 2) is described.

FIGS. 38A-38F show each example of the element range of the complexarray in the complex array generation unit in the third embodiment ofthe present invention. FIGS. 38A, B and C show examples of the range ofelements of the complex array in the complex array generation unit 112,and show examples in the case using two-dimensional complex array inN=3. In FIGS. 38A-38F, the rectangular part indicates the complex array,and the shaded region indicates the range of elements where assignmentof the embedding sequence should be performed.

Since inverse Fourier transform is performed on the complex array in theN−1-dimensional Fourier transform unit 113 later, the complex array canbe considered to be representation for the embedding pattern in thefrequency domain.

Since the element (0, 0) of the array indicates the DC component, bycyclically rewriting the complex array such that the element (0, 0) ofthe array becomes the center, it can be understood which frequency bandis used for embedding the embedding sequence 913 as shown in FIGS. 38D,E and F.

FIG. 38D shows a rectangular region, FIG. 38E shows a circle region, andFIG. 38F shows a rhombus region, and embedding is performed into anintermediate frequency band in each of them.

For example, considering digital watermark embedding into an image or avideo, it can be considered that digital watermark embedded in a highfrequency region is easily deleted due to video coding such as MPEG2 orH.264. On the other hand, since embedding into a low frequency regionhas large visual effect. Thus, embedding into intermediate frequencyband is taken as an example.

In addition, from the viewpoint of human visual feature, it is knownthat, in high frequency region, visual sensitivity for diagonaldirection frequency is lower than that for vertical and horizontaldirection frequency (Makoto Miyahara, “Systematic image coding”,Industrial Publishing & Consulting, Inc, 1990, pp. 87), so that thediagonal direction frequency has a feature in that it is indistinctivealthough it is embedded in low frequency band compared with the verticaland horizontal direction. In addition, for example, since a quantizationstep in the diagonal direction in image/video coding and the like suchas JPEG and MPEG is set to be larger than the vertical and horizontaldirection, there is a tendency that high frequency is decreased due tocoding more easily in the diagonal direction compared with the verticaland horizontal direction. In spite of such a situation, by performingembedding in the rhombus region as shown in FIGS. 38C and F, digitalwatermark embedding can be performed in which image quality is high androbustness is high.

FIGS. 39A-39F show each example of the element region of the complexarray in the complex array generation unit in the third embodiment ofthe present invention. In the case of digital watermark embedding into avideo, when digital watermark detection of high detection performance isperformed using a long term signal in the time direction like thepresent invention, that is, using many frames, the strength forembedding digital watermark can be made small. As a result, althoughembedding is performed into low frequency region as shown in FIGS.39A-39F, visual effect can be decreased, and such embedding method canbe adopted.

<Digital Watermark Embedding Apparatus—Complex Pattern GenerationUnit—N−1-Dimensional Inverse Fourier Transform Unit>

Next, operation of the N−1-dimensional inverse Fourier transform unit113 of the complex pattern generation unit 110 b is described in detail.

Fourier transform in the N−1-dimensional inverse Fourier transform unit113 is performed according to the following procedure.

1) Assuming that the N−1-dimensional intermediate complex pattern 904generated by the complex array generation unit 112 is A[x₁, x₂, . . . ,x_(N−1)].

2) N−1-dimensional discrete inverse Fourier transform is performed onA(x_(i), x₂, . . . , x_(N−1)) to obtain the embedding complex patternP(x₁, x₂, . . . , x_(N−1)),

$\begin{matrix}{{P\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1}} \right)} = {\frac{1}{\sqrt{M_{1}M_{2}\mspace{14mu}\ldots\mspace{14mu} M_{N - 1}}}{\sum\limits_{u_{1} = 0}^{M_{1} - 1}\;{\sum\limits_{u_{2} = 0}^{M_{2} - 1}\mspace{14mu}{\ldots\mspace{14mu}{\sum\limits_{{u_{N} - 1} = 0}^{M_{N - 1} - 1}\;{{A\left\lbrack {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1}} \right\rbrack}{{\mathbb{e}}^{j2\pi}\left( {\frac{x_{1}u_{1}}{M_{1}} + \frac{x_{2}u_{2}}{M_{2}} + \ldots + \frac{x_{N - 1}u_{N - 1}}{M_{N - 1}}} \right)}}}}}}}} & (86)\end{matrix}$wherein M₁, M₂, . . . , M_(N−1) indicate sizes (number of elements ofeach dimension) of the N−1-dimensional intermediate complex pattern 904generated in the complex array generation unit 112.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit>

Next, the detection information extraction unit 220 b of the digitalwatermark detection apparatus 200 in the third embodiment is described.

FIG. 40 shows a configuration example of the detection informationextraction unit in the third embodiment of the present invention.

The detection information process unit 220 b shown in the figureincludes a N−1-dimensional Fourier transform unit 225, a detectionsequence extraction unit 221, a correlation value calculation unit 222,a maximum value determination unit 223, and a detection informationreconfiguration unit 224, and the unit 220 b receives the detectioncomplex pattern 961 and outputs detection information 914.

By the way, in FIG. 40, please note that the configuration is shown suchthat information flows from the bottom to the top to facilitateunderstanding of correspondence to FIG. 36.

Detection information extraction processes by the detection informationextraction unit 220 b are performed in the following procedure.

FIG. 41 is a flowchart of operation of the detection informationextraction unit in the third embodiment of the present invention.

Step 1201) The N−1-dimensional Fourier transform unit 225 performsN−1-dimensional Fourier transform on the received detection complexpattern 961 to generate the N−1-dimensional detection complex array 1115similarly.

Details of operation of the N−1-dimensional Fourier transform unit 225are described later.

Step 1202) The detection sequence extraction unit 221 configures thedetection sequence 1113 by extracting and arranging the values of thereal part and the imaginary part of the element value from the detectioncomplex array 1115 generated by the N−1-dimensional Fourier transformunit 225.

Details of operation of the detection sequence extraction unit 221 aredescribed later.

Step 1203) The correlation value calculation unit 222 calculatescorrelation between the detection sequence 1113 configured by thedetection sequence extraction unit 221 and embedding sequencesconfigured based on assumed embedding sequences so as to obtain thecorrelation values 1114.

Operation of the correlation value calculation unit 222 is the same asthat in the first embodiment.

Step 1204) The maximum value determination unit 223 finds a maximumcorrelation value in the correlation values 1114 obtained by thecorrelation value calculation unit 222 to determine an embeddingsequence used for correlation calculation in the correlation valuecalculation unit 222 corresponding to the maximum correlation value1114.

The operation of the maximum value determination unit 223 is the same asthat in the first embodiment. Depending on the configuration method forthe embedding sequence in the digital watermark embedding apparatus 100,it is needless to say that determination may be performed using othermethod instead of the maximum value determination by the maximum valuedetermination unit 223.

Step 1205) The detection information reconfiguration unit 224reconfigures detection information 914 that is determined to be actuallyembedded based on the embedding sequence determined by the maximum valuedetermination unit 223.

The operation of the detection information reconfiguration unit 224 isthe same as that in the first embodiment.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—N−1-Dimensional Inverse Fourier Transform Unit>

Next, details of operation of the N−1-dimensional Fourier transform unit225 of the detection information extraction unit 220 b are described.

Fourier transform processes in the N−1-dimensional Fourier transformunit 225 are performed according to the following procedure.

1) N−1-dimensional complex array of the size of M₁×M₂× . . . ×M_(N−1) isconfigured from the received detection complex pattern 961, in which M₁,M₂, . . . , M_(N−1) are element numbers similar to those used in thecomplex array generation unit 112 of the digital watermark embeddingapparatus 100.

When the detection complex pattern 961 is obtained as a discrete signal,it is regarded as the N−1-dimensional complex array as it is. When thedetection complex pattern 961 is obtained as a continuous signal, dataobtained by sampling the detection complex pattern 961 using arbitrarysampling means is used as the N−1-dimensional complex array.

2) Assuming that the complex array in 1) is Q(x₁, x₂, . . . , x_(N−1)),N−1-dimensional discrete Fourier transform is performed on Q(x₁, x₂, . .. , x_(N−1)) to obtain A[u₁, u₂, . . . , u_(N−1)].

$\begin{matrix}{{A\left\lbrack {u_{1},u_{2},\ldots\mspace{14mu},u_{N - 1}} \right\rbrack} = {\frac{1}{\sqrt{M_{1}M_{2}\mspace{14mu}\ldots\mspace{14mu} M_{N - 1}}}{\sum\limits_{x_{1} = 0}^{M_{1} - 1}\;{\sum\limits_{x_{2} = 0}^{M_{2} - 1}\mspace{14mu}{\ldots\mspace{14mu}{\sum\limits_{{x_{N} - 1} = 0}^{M_{N - 1} - 1}{{Q\left( {x_{1},x_{2},\ldots\mspace{14mu},x_{N - 1}} \right)}{{\mathbb{e}}^{- {j2\pi}}\left( {\frac{x_{1}u_{1}}{M_{1}} + \frac{x_{2}u_{2}}{M_{2}} + \ldots + \frac{x_{N - 1}u_{N - 1}}{M_{N - 1}}} \right)}}}}}}}} & (87)\end{matrix}$

3) A[u_(i), u₂, . . . , u_(N−1)] obtained in 2) is output to thedetection sequence extraction unit 221 as the detection complex array1115.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—Detection Sequence Extraction Unit>

Next, details of operation of the detection sequence extraction unit 220b of the detection information extraction unit 221 are described.

Although the operation of the detection sequence extraction unit 221 isbasically the same as that in the first embodiment, processes may beperformed as follows in accordance with the operation of the complexarray generation unit 112.

1) Elements within the range used in the complex array generation unit112 of the digital watermark embedding apparatus 100 are extracted fromthe detection complex array 1115 obtained by the N−1-dimensional Fouriertransform unit 225, and the real part and the imaginary part of theextracted complex number values are arranged by regarding each of thereal part and the imaginary part as an independent real number value.This process is a symmetrical process with respect to generation of thecomplex array in the complex array generation unit 112 of the digitalwatermark embedding apparatus 100.

2) Assuming that the obtained sequence is i″₁, i″₂, . . . , i″_(L), andthe sequence is output as the detection sequence 1113.

When order of the embedding sequence 913 or elements of the complexarray has been permuted in the complex array generation unit 112 of thedigital watermark embedding apparatus 100, the order is restored in thesame way as the first embodiment.

<Characteristics of the Third Embodiment>

In the following, characteristics of the present embodiment aredescribed.

According to the digital watermark embedding apparatus and the digitalwatermark detection apparatus of the present embodiment, like one shownin the patent document 1, for examine, since digital watermark can beembedded in a band in which the watermark easily remains even in codingor noise addition in a video signal and visual effect is small, digitalwatermark embedding in which robustness is high and image quality ishigh becomes possible.

Especially, by using the rhombus region as the region for embedding inthe frequency domain, digital watermark embedding that is more robustfor compression in video coding and the like becomes possible.

In addition, since the embedding pattern is spread over the wholesignal, by adopting offset search method disclosed in the patentdocument 1, digital watermark detection becomes possible even from asignal that is partially cut from the embedded signal.

Further, in the present invention, different from the digital watermarkscheme shown in the patent document 1, since the intermediate complexpattern 904 does not need to maintain symmetrical property of Fouriertransform coefficients, an embedding sequence 913 two times longer canbe embedded compared with a watermark coefficient matrix and the likedescribed in paragraph number 0197 in the patent document 1. That is, aspectrum spread sequence length twice as long as the conventional onecan be used.

As describe before, as the spectrum spread sequence length increases,detection with high reliability becomes possible. In addition, in thecase of detection reliability similar to conventional techniques, theembedding information length can be doubled. In addition, in the case ofdetection reliability and information length both similar toconventional techniques, digital watermark embedding with less qualitydeterioration becomes possible. Thus, according to the presentinvention, digital watermark embedding becomes possible in whichreliability is high, information length is long and qualitydeterioration is small.

In addition, the present embodiment and the temporal modulation unit 130b or the temporal demodulation unit 210 b of the second embodiment canbe combined and carried out.

When combining the present embodiment and the temporal modulation unit130 b or the temporal demodulation unit 210 b of the second embodiment,N−1-dimensional inverse Fourier transform process of the N−1-dimensionalinverse Fourier transform unit 113 and the one-dimensional inverseFourier transform process of the temporal modulation unit 130 may beperformed together as N-dimensional inverse Fourier transform process.In the same way, N−1-dimensional transform process of theN−1-dimensional Fourier transform unit 225 and the one-dimensionalFourier transform process of the temporal demodulation unit 210 may beperformed together as N-dimensional Fourier transform process.

[Fourth Embodiment]

<Temporal Synchronization Unnecessary Detection<

In the following, a digital watermark embedding apparatus and a digitalwatermark detection apparatus of the fourth embodiment are described.

The present embodiment is an example in which, when digital watermarkembedding is performed by using the digital watermark embeddingapparatus 100 in the first embodiment, the digital watermark detectionapparatus performs digital watermark detection without necessity toperform synchronization when signals desynchronized in the time axis(N-th dimension axis) direction are received.

The digital watermark detection apparatus of the present embodiment hasa configuration similar to that of the digital watermark detectionapparatus 200 of the first embodiment, and only the detectioninformation extraction unit 220 has a different configuration.

As to the temporal demodulation unit 210, a temporal demodulation unitof other embodiments of the present invention may be used. For example,the temporal demodulation units 210 b and 210 c of the second embodimentmay be used.

By the way, although the present embodiment is described by taking, asan example, the case where digital watermark embedding is performed bythe digital watermark embedding apparatus 100 of the first embodiment,the present embodiment can be also applied to detection in the case whendigital watermark embedding is performed using a digital watermarkembedding apparatus in other embodiments by similarly combining. Forexample, digital watermark embedding may be performed by the digitalwatermark embedding apparatus in the third embodiment, and detection maybe performed by combining the N−1-dimensional Fourier transform unit 225of the digital watermark detection apparatus in the third embodiment. Inthese cases, although there is a case in which modificationcorresponding to individual procedures is necessary, it is needless tosay that the necessary modifications are obvious based on descriptionsof the present embodiment and descriptions of digital watermarkembedding in the embodiments.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit>

In the following, operation of the detection information extraction unitin the digital watermark detection apparatus of the present embodimentis described.

FIG. 42 shows a configuration of the detection information extractionunit in the fourth embodiment of the present invention. In the figure,same signs are provided for same configuration parts in FIGS. 28 and 40.

The detection information extraction unit 220C shown in the figureincludes the detection sequence extraction unit 221, the complexcorrelation value calculation unit 226, an absolute value calculationunit 227, a maximum value determination unit 223, and the detectioninformation reconfiguration unit 224, and the unit 220 c receives thedetection complex pattern 961 and outputs the detection information 914.

The detection information extraction processes by the detectioninformation extraction unit 220 c are performed according to thefollowing procedure.

FIG. 43 shows a flowchart of the operation of the detection informationextraction unit in the fourth embodiment of the present invention.

Step 1301) The detection sequence extraction unit 221 configures thedetection complex number sequence 1118 in which complex number valuesobtained from the received detection complex pattern 961 are arranged.Detailed operation of the detection sequence extraction unit 221 aredescribed later.

Step 1302) The complex correlation value calculation unit 226 calculatescomplex correlation between the detection complex number sequence 1118configured by the detection sequence extraction unit 221 and the complexnumber sequences configured based on assumed embedding sequences toobtain the complex correlation values 1116 represented by complexnumbers.

When different values are embedded depending on the kind of embeddingsequence, complex correlation is calculated for each of the plurality ofcomplex number sequences configured based on a plurality of conceivableembedding sequences so as to obtain a corresponding complex correlationvalue 1116.

Details of the operation of the complex correlation value calculationunit 226 are described later.

Step 1303) The absolute value calculation unit 227 calculates absolutevalues 1117 of the complex correlation values 1116 obtained by thecomplex correlation value calculation unit 226. By calculating theabsolute value, it becomes possible to determine an embedding sequencehaving high correlation with the detection complex number sequenceirrespective of the amount of desynchronization even when desynchronizedsignal is received.

Step 1304) The maximum value determination unit 223 finds maximum one ofthe absolute values 1117 obtained by the absolute value calculation unit227, and determines an embedding sequence used for correlationcalculation in the complex correlation value calculation unit 226corresponding to the maximum absolute value.

By the way, depending on the method for configuring the embeddingsequence in the digital watermark embedding apparatus 100, determinationmay be performed using other method instead of the maximum valuedetermination by the maximum value determination unit 223.

Details of operation of the maximum value determination unit 223, anddetails of alternative methods are described later.

Step 1305) The detection information reconfiguration unit 224reconfigures the detection information 914 that is determined to beactually embedded based on the embedding sequence determined in themaximum value determination unit 223.

Operation of the detection information reconfiguration unit 224 is thesame as that of the first embodiment.

By the way, when embedding of the digital watermark is performed usingthe digital watermark embedding apparatus 100 of the third embodiment,Fourier transform process is necessary like the N−1-dimensional Fouriertransform unit 225 in the third embodiment before the detection sequenceextraction unit 221.

In addition, after determining the embedding sequence by the maximumvalue determination unit 223, by using the embedding sequence, processessimilar to the detection information extraction unit 220 a in the firstembodiment may be performed in a round-robin fashion using signalsobtained by sequentially desynchronizing the input signal so as tomeasure the desynchronization amount and obtain a more accuratedetection correlation evaluation value based on the correlation valueobtained by the detection information extraction unit 220. It isneedless to say that it becomes possible, by using this method, toperform detection at speed much higher than a case for searching allamounts pf desynchronization for conceivable all embedding sequences ina round-robin fashion.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—Detection Sequence Extraction Unit>

Next, details of operation of the detection sequence extraction unit 221of the detection information extraction unit 220 c are described.

The detection sequence extraction unit 221 configures the detectioncomplex number sequence from the complex number values obtained from thedetection complex pattern 961.

Processes in the detection sequence extraction unit 221 are performedaccording to the following procedure.

1) A N−1-dimensional complex array of the size of M₁×M₂× . . . ×M_(N−1)are configured from the detection complex pattern 961. The method forconfiguring is the same as the process in step 801 shown in FIG. 30 inthe before-mentioned first embodiment.

2) The complex number values are extracted one by one sequentially fromthe complex array obtained in 1) to be arranged as the detection complexnumber sequence 1118. That is, when the complex array is represented asA[p₁, p₂, . . . , p_(N−1)](p_(n)≧0), and the detection complex numbersequence 1118 is represented as i″₁, i″₂, . . . , i″_(N−1),

$\begin{matrix}{{i_{1}^{''} = {A\left\lbrack {0,0,\ldots\mspace{14mu},0} \right\rbrack}}{i_{2}^{''} = {A\left\lbrack {1,0,\ldots\mspace{14mu},0} \right\rbrack}}\vdots} & (88)\end{matrix}$

3) The obtained sequence i″₁, i″₂, . . . , i″_(L) is output as thedetection sequence 1115.

When order of the embedding sequence 913 or elements of the complexarray has been permuted in the complex array generation unit 112 of thedigital watermark embedding apparatus 100, the order is restored in thesame way as the detection sequence extraction unit 221 in the firstembodiment.

By the way, when the digital watermark embedding has been performedusing the digital watermark embedding apparatus 100 of the thirdembodiment, complex number values of elements within the range that isused in the complex array generation unit 112 of the digital watermarkembedding apparatus 100 in the third embodiment are extracted andarranged in the above-mentioned 2).

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—Complex Correlation Value Calculation Unit>

Next, details of operation of the complex correlation value calculationunit 226 of the detection information extraction unit 220 c aredescribed.

Complex correlation value calculation processes in the complexcorrelation value calculation unit 226 are performed according to thefollowing procedure.

1) Conceivable embedding sequences w⁽¹⁾, w⁽²⁾, . . . are generated by aprocedure similar to that in the embedding sequence generation unit 111of the digital watermark embedding apparatus 100. The method forgeneration is the same as that in the correlation value calculation unit222 in the before-mentioned first embodiment.

2) From the embedding sequences w⁽¹⁾, w⁽²⁾, . . . obtained from 1),values that are assigned to the real part and the imaginary part of acomplex number value in the complex array generation unit 112 of thedigital watermark embedding apparatus 100 are paired so that similarcomplex number sequence is configured as the embedding complex numbersequence ξ⁽¹⁾, ξ⁽²⁾, . . . . That is, when the complex array isconfigured like FIG. 17,

assuming

$\begin{matrix}{{{w^{(k)} = \left\{ {w_{1}^{(k)},w_{2}^{(k)},\ldots\mspace{14mu},w_{L}^{(k)}} \right\}},{\xi^{(k)} = {\left\{ {\xi_{1}^{(k)},\xi_{2}^{(k)},\ldots\mspace{14mu},\xi_{L^{\prime}}^{(k)}} \right\}\left( {L^{\prime} = {L/2}} \right)}}}{\xi_{1}^{(k)} = {w_{1}^{(k)} + {j\; w_{2}^{(k)}}}}{\xi_{2}^{(k)} = {w_{3}^{(k)} + {j\; w_{4}^{(k)}}}}\vdots{\xi_{L^{\prime}}^{(k)} = {w_{L - 1}^{(k)} + {j\; w_{L}^{(k)}}}}} & (89)\end{matrix}$

The configuration method for the embedding complex number sequence isnot limited to this example, and it is needless to say that anyconfiguration method can be used as long as it is adapted to theconfiguration of the complex array in the complex array generation unit112 of the digital watermark embedding apparatus 100.

3) Correlation between the detection sequence 1115 obtained in thedetection sequence extraction unit 221 and each of embedding sequencesξ⁽¹⁾, ξ⁽²⁾, . . . obtained in 2) is calculated using complexcorrelation.

Correlation calculation is performed as follows. Assuming that ρ^((j))is the complex correlation value 1116 desired to be obtained,

$\begin{matrix}{\rho^{(j)} = {{i^{''} \cdot \xi^{{(j)}*}} = {\sum\limits_{k = 1}^{L^{\prime}}\;{i_{k}^{''}\xi_{k}^{{(j)}*}}}}} & (90)\end{matrix}$wherein ξ^((j)*) indicates a number sequence including the conjugatecomplex number of the element of ξ^((j)), and ξ_(k) ^((j)*) is aconjugate complex number of ξ_(k) ^((j)). In addition, “·” indicatesinner product operation when the number sequence is regarded as avector. Here, ρ^((j)) becomes a complex number.

For aligning evaluation criteria of detection reliability described inthe before-mentioned document—Takao Nakamura, Atsushi Katayama, MasashiYamamuro, Noboru Sonehara, “Fast Watermark Detection Scheme from AnalogImage for Camera-equipped Cellular Phone”, IEICE Transactions D-II, Vol.j87-D-II, No. 12, pp. 2145-2155, 2004—, each element of i″ and w^((j))may be normalized beforehand such that the average becomes 0 and thatthe variance becomes 1 so that calculation may be performed bymultiplying by a constant term in the correlation value calculation inthe same way in the correlation value calculation unit 222 of the firstembodiment.

In the following, it is described that, by such operation, digitalwatermark detection is possible for desynchronized inputs.

Assuming that a sequence embedded by the digital watermark embeddingapparatus is w={w₁, w₂, . . . , w_(L)}, and that a sequence obtained byarranging w as complex numbers is ξ={ξ₁, ξ₂, . . . , ξ_(L′)}.

When a complex sequence after a before-embedding signal and other noisesignal are added by digital watermark embedding is i′={i₁, i₂, . . . ,i_(L′)},i′=i+ξ  (91)is obtained.

In addition, when assuming that a sequence obtained afterdesynchronization in the time direction is applied to i′ is i″,i″=i′e^(jΔe)  (92) is obtained.

When correlation with ξ is calculated using the above equation,

$\begin{matrix}\begin{matrix}{\rho = {i^{''} \cdot \xi^{*}}} \\{= {\left( {i + \xi} \right){{\mathbb{e}}^{j\Delta\theta} \cdot \xi^{*}}}} \\{= {{\mathbb{e}}^{j\Delta\theta}\left( {{i \cdot \xi^{*}} + {\xi \cdot \xi}} \right)}} \\{= {{\mathbb{e}}^{j\Delta\theta}\left( {{\sum\limits_{k = 1}^{L^{\prime}}\;{i_{k}\xi_{k}^{*}}} + {\sum\limits_{k = 1}^{L^{\prime}}{\xi_{k}\xi_{k}^{*}}}} \right)}} \\{= {{\mathbb{e}}^{j\Delta\theta}\left( {{\sum\limits_{k = 1}^{L^{\prime}}\;{i_{k}\xi_{k}^{*}}} + {\sum\limits_{k = 1}^{L^{\prime}}{\xi_{k}}^{2}}} \right)}}\end{matrix} & (93)\end{matrix}$is obtained. When i and ξ are independent, and when L′ is large enough,an expected value ofΣi_(k)ξ_(k)*is 0, and

$\begin{matrix}{\rho \sim {\left( {\sum\limits_{k = 1}^{L^{\prime}}{\xi_{k}}^{2}} \right){\mathbb{e}}^{j\Delta\theta}}} & (94)\end{matrix}$is obtained, so that

$\begin{matrix}{{\rho } \sim {\sum\limits_{k = 1}^{L^{\prime}}{\xi_{k}}^{2}}} & (95)\end{matrix}$is obtained.

On the other hand, when digital watermark is not embedded,

$\begin{matrix}{\rho = {\sum\limits_{k = 1}^{L^{\prime}}{i_{k}\xi_{k}^{*}}}} & (96)\end{matrix}$holds true, and since an expected value of this is 0, |ρ| issufficiently small compared with the expected value

$\sum\limits_{k = 1}^{L^{\prime}}{\xi_{k}}^{2}$obtained when digital watermark is embedded, so that digital watermarkdetection becomes possible.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—Maximum Value Determination Unit>

Next, the maximum value determination unit 223 of the detectioninformation extraction unit 220 c is described in detail.

Processes in the maximum value determination unit 223 are performedaccording to the following procedure.

1) The maximum value determination unit 227 finds an absolute value|ρ^((j))| having a maximum value from absolute values 1117 |ρ⁽¹⁾|,|ρ⁽²⁾|, . . . obtained by the absolute value calculation unit 227 asfollows.|ρ^((max))|=MAX(|ρ⁽¹⁾|,|ρ⁽²⁾|, . . . )  (97)

2) An embedding sequence w^((max)) corresponding to |ρ^((max))| isobtained.

In addition, it may be determined whether the maximum correlation value|^((j))| exceeds a predetermined threshold, and when the maximumcorrelation value does not exceed the predetermined threshold, it may bedetermined that digital watermark is not embedded.

In the following, alternative operation of the maximum valuedetermination unit 223 is described.

Instead of the maximum value determination by the maximum valuedetermination unit 223, without calculating complex correlation forcomplex sequences corresponding to every embedding sequence w⁽¹⁾, w⁽²⁾,. . . in the complex correlation value calculation unit 226, correlationmay be calculated from the complex number sequence ξ⁽¹⁾ corresponding tothe embedding sequence w⁽¹⁾ sequentially to perform determination basedon whether the absolute value of the obtained complex correlation valueexceeds a predetermined threshold, and to determine an embeddingsequence by which the correlation value exceeds the threshold asw^((max)) and ends correlation calculation at that time.

In addition, when the embedding sequence in the digital embeddingapparatus 100 is embedded by being configured only by one kind ofembedding sequence like one shown in (example 1) of the embeddingsequence generation unit 111, or for example, when it is embedded bybeing configured based on difference of plus and minus of one kind ofembedding sequence like one shown in (example 2), (example 4) of theembedding sequence generation unit 111, maximum value determination bythe maximum value determination unit 223 has no meaning since only onecorrelation value is calculated. Instead, determination may be performedbased on whether the obtained correlation value exceeds thepredetermined threshold.

In addition, reliability of the watermark detection may be evaluatedbased on the size of the absolute value of the complex correlationvalue.

When the embedding sequence in the digital watermark embedding apparatus100 is configured and embedded so as to represent 0/1 of a bit valuebased on difference between plus and minus of the embedding sequence asshown in (example 2), (example 4) of the embedding sequence generationunit 111, a case in which a signal having a phase shifted by halfwavelength due to desynchronization is received cannot be distinguishedfrom a case in which information in which all bit values are reversed isembedded. In such a case, for example, the embedding sequence may beconfigured such that one bit in bit values always has 1 (or 0) as a bitfor judgment so that bit reversal may be corrected using the bit value.In addition, the judgment may be made by performing coding usingasymmetric error correcting code. In addition, determination may beperformed using a digital watermark signal different from the digitalwatermark of the present invention. The method is not limited to theseexamples, and it is needless to say that correction of bit reversal maybe performed by other method.

In addition, when spreading is performed based on polarity of plus andminus for each bit by using a partial sequence of the embedding sequencelike (example 4) in the embedding sequence generation unit 111, morerobust detection process can be performed as follows.

It is assumed that a partial complex sequence corresponding to a-th bitposition in the detection complex number sequence 1118 isi^(n(a))=(i_(i) ^(n(a)),i₂ ^(n(a)), . . . i_(m) ^(n(a)))In addition, it is assumed that a complex embedding sequence used forspreading for a bit value on the a-th bit position isξ^((a))=(ξ₁ ^((a)),ξ₂ ^((a)), . . . ξ_(m) ^((a))).Then, a complex correlation value λ^((a)) is calculated for each bitposition a as follows.

$\lambda^{(a)} = {{i^{''{(a)}} \cdot \xi^{{(a)}*}} = {\sum\limits_{s = 1}^{m}\;{i_{s}^{''{(a)}}\xi_{s}^{{(a)}*}\mspace{50mu}\left( {a = {1\mspace{14mu}\ldots\mspace{14mu} n}} \right)}}}$

Next, directions of n complex correlation values λ^((a)) are aligned.More particularly, for example, λ^((a)) that satisfies 0≦Argλ^((a))<π isnot changed, and λ^((a)) that satisfies π≦Argλ^((a))<2π is multiplied bye^(jπ) so that the argument is rotated by 180 degrees. By this changingprocess, every λ^((a)) becomes a value within the first and secondquadrants on the complex plane. By the way, the method for aligningdirections is not limited to this example. For example, it is obviousthat a method can be configured such that every λ^((a)) becomes a valuewithin the first and fourth quadrants on the complex plane.

Next, a total sum λ of the complex correlation values λ^((a)) on whichthe above-mentioned changing process has been performed is obtained asfollows.

$\lambda = {\sum\limits_{a = 1}^{n}\;\lambda^{(a)}}$

Then, the complex plane is divided into two regions using a straightline that passes through an origin point and that is orthogonal to Arg λas a boundary line on the complex plane, and a detection bit value ofthe a-th bit position is determined based on a region λ^((a)) before thechanging process belongs to between the two regions. Although thisdetermining method also includes the above-mentioned uncertainty of bitreversal, the uncertainty can be solved by using one bit of bits valuesas a flag for determining bit reversal, for example.

For example, in the case when n=2, as shown in FIG. 44, since 0≦Argλ⁽¹⁾<π is satisfied, λ⁽¹⁾ is not changed, and since π≦Argλ⁽²⁾<2π issatisfied, λ⁽²⁾ is multiplied by e^(jπ) so that the argument is rotatedby 180 degrees. Then, the total sum λ of these are obtained, and thecomplex plane is divided into two regions using a straight line thatpasses through the origin point and that is orthogonal to Argλ as aboundary line on the complex plane, and the bit value of one region isdetermined to be “1” and the bit value of another region is determinedto be “0”, so that a detection bit value of each bit position isdetermined based on which region λ⁽¹⁾ or λ⁽²⁾ before changing processbelongs to between the two regions.

The reason that the above-mentioned detection method works well isdescribed below. When embedding, modulation is performed by multiplyingthe complex embedding sequence for each bit position by +1 or −1according to the bit value. Thus, the complex correlation value λ^((a))for each bit position has a value in which the phase is shifted by πwhen the embedded bit value is different. However, by equating the phaseshift of π, all of λ^((a)) align in the direction of phase shift amountΔθ of the input signal. It is obvious that the above-mentioned changingprocess can be performed as the method of equating.

In addition, the length m of the complex embedding sequence for each bitis shorter than the length L′ of the whole of the complex embeddingsequence. That is, since spreading ratio of the complex embeddingsequence for each bit is low so that only a gain by the spreading rationm is obtained when a bit value of each bit is detected, robustnessbecomes low. However, by obtaining the total sum λ after aligning thedirections of all λ^((a)) by performing the change in which phase shiftsof π are equated as mentioned above, gain corresponding to the wholeembedding sequence length L′ can be obtained. Therefore, by evaluatingagain each λ^((a)) before change using the boundary line orthogonal toArgλ so as to detect detection bit value, bit determination errorbecomes smaller compared with the case in which detection is performedfor each bit, so that higher robustness can be realized. By the way, thereliability of the digital watermark detection may be evaluated by thesize of the absolute value of λ.

<Characteristics of the Fourth Embodiment>

Next, characteristics of the fourth embodiment are described.

According to the digital watermark detection apparatus of the presentembodiment, in detection of digital watermark, even when the signal ofthe digital watermark detection target is desynchronized, detection ofdigital watermark can be performed. That is, by utilizing a fact thatthe embedding sequence that are spectrum spread in the N−1-dimensionalspace is commonly affected by desynchronization in a direction of N-thdimension, digital watermark detection in which synchronization isunnecessary can be performed by using the complex correlation value ofthe spread sequence in the N−1-dimensional space.

For example, in the case of video signals, digital watermark detectionis possible without using a special synchronization method even when aframe for starting detection is shifted in the time direction. This isvery effective in a use situation in which temporal synchronization isdifficult, such as when detecting digital watermark from a video thatwas re-taken using a video camera and the like, and when detectingdigital watermark from a video that is converted to analog data such asa video tape, for example.

When a video displayed on a screen or TV or the like is taken by a videocamera or a camera of a cellular phone and the like, since the framerate for reproduction is not synchronized with the frame rate fortaking, there is a case in which re-sampling may occur in sub-frames.This indicates a state in which desynchronization occurs in sub-framelevel (interval shorter than one frame) as a result. Even in such asituation, it is possible to measure the phase of the periodic signal intemporal demodulation, and as mentioned above, digital watermarkdetection in which synchronization is unnecessary becomes possible.

By the above-mentioned digital watermark detection, efficient detectionis possible for desynchronized signals, and in addition to that, it isunnecessary to add a special synchronization signal. Thus, digitalwatermark detection becomes possible without signal deterioration due tothe synchronization signal and without deterioration of detectionperformance of digital watermark in which quality is high and detectionperformance is high.

[Fifth Embodiment]

<Measurement of Amount of Desynchronization>

In the following, a digital watermark detection apparatus in the fifthembodiment is described.

This embodiment is an example in which, in the case when digitalwatermark embedding is performed using the digital watermark embeddingapparatus 100 in the first embodiment of the present invention, when thedigital watermark detection apparatus receives a signal that isdesynchronized in the time axis (axis of N-th dimension), the digitalwatermark detection apparatus detects the amount of desynchronization todetect digital watermark.

By the way, in the present embodiment, although an example is describedfor the case when digital watermark embedding is performed using thedigital watermark embedding apparatus 100 of the first embodiment, thepresent embodiment can be also combined and applied similarly to a casein which digital watermark embedding is performed using a digitalwatermark embedding apparatus of other embodiments. For example, it maybe possible to perform embedding using the digital watermark embeddingapparatus in the third embodiment and perform detection by combining theN−1-dimensional Fourier transform unit 225 in the digital watermarkdetection apparatus of the third embodiment. In these cases, althoughthere may be a case in which modification corresponding to individualprocedure is necessary, it is needless to say that these necessarymodifications are obvious based on descriptions of the presentembodiment and descriptions of the digital watermark embedding.

<Digital Watermark Detection Apparatus>

Configuration of the digital watermark detection apparatus of thepresent embodiment is described.

FIG. 45 shows a configuration example of the digital watermark detectionapparatus in the fifth embodiment of the present invention.

The digital watermark detection apparatus 300 shown in the figureincludes a temporal demodulation unit 310, a synchronization detectionunit 320, a detection information extraction unit 330 a, a patternstorage unit 340, and the digital watermark detection apparatus 300receives the embedded signal 923 and outputs detection information 914.

The temporal demodulation unit 310 is the same as the temporaldemodulation unit 210 in the first embodiment. In addition, temporaldemodulation units of other embodiments may be used. For example, thetemporal demodulation units 210 c, 210 d in the second embodiment may beused.

By the way, in FIG. 45, please note that the configuration is shown suchthat information flows from the bottom to the top to facilitateunderstanding of correspondence to FIG. 10.

Digital watermark detection processes by the digital watermark detectionapparatus 300 are performed in the following procedure.

FIG. 46 is a flowchart showing operation of the digital watermarkdetection apparatus in the fifth embodiment of the present invention.

Step 1401) The temporal demodulation unit 310 performs demodulation inthe time axis direction to obtain a detection complex pattern 1501 andstores it into the pattern storage unit 340. Content of the processes isthe same as that in the temporal demodulation unit 210 of the digitalwatermark detection apparatus 200 of the first embodiment.

By the way, like the digital watermark detection apparatus 200 of thefirst embodiment, pre-process may be performed on the embedded signal923 before temporal demodulation process by the temporal demodulationunit 310.

Step 1402) From the detection complex pattern 1501 that is obtained bythe temporal demodulation unit 310 and that is stored in the patternstorage unit 340, the synchronization detection unit 320 detects theamount of desynchronization in the time axis (axis of N-th dimension)direction that is applied to the embedded signal 923 beforehand, so asto outputs it as the amount of desynchronization.

Details of operation of the synchronization detection unit 320 aredescribed later.

Step 1403) The detection information extraction unit 330 a analyzes thedetection complex pattern that is obtained in the temporal demodulationunit 310 and that is stored in the pattern storage unit 340, andextracts digital watermark information, that is embedded in the digitalwatermark embedding apparatus 100, based on the amount ofdesynchronization 1502 obtained by the synchronization detection unit320, and outputs it as the detection information 914.

Details of the operation of the detection information extraction unit330 a are described later.

<Digital Watermark Detection Apparatus—Synchronization Detection Unit>

Next, details of operation of the synchronization detection unit 320 aredescribed.

FIG. 47 shows a configuration example of the synchronization detectionunit in the fifth embodiment of the present invention.

The synchronization detection unit 320 includes a complex detectionsequence extraction unit 321, a complex correlation value calculationunit 322, an absolute value calculation unit 323, a synchronizationdetection maximum value determination unit 324, a phase calculation unit325, and the synchronization detection unit 320 reads the detectioncomplex pattern 1501 from the pattern storage unit 340 and outputs theamount of desynchronization 1502.

By the way, in FIG. 47, please note that the configuration is shown suchthat information flows from the bottom to the top to facilitateunderstanding of correspondence to FIG. 45.

Synchronization detection processes by the synchronization detectionunit 320 are performed according to the following procedure.

FIG. 48 is a flowchart of operation of the synchronization detectionunit in the fifth embodiment of the present invention.

Step 1501) The complex detection sequence extraction unit 321 configuresa detection complex number sequence 1511 obtained by arranging complexnumber values that are obtained from the received detection complexpattern 1501.

Operation of the complex detection sequence extraction unit 321 is thesame as operation of the detection sequence extraction unit 221 in thedigital watermark detection apparatus 200 of the fourth embodiment.

Step 1502) The complex correlation value calculation unit 322 calculatescomplex correlation between the detection complex number sequence 1511configured by the detection sequence extraction unit 321 and the complexnumber sequences configured based on the assumed embedding sequences toobtain the complex correlation values 1512 that are represented bycomplex numbers.

In the case when different values are embedded according to the type ofthe embedding sequence, complex correlation is calculated for each of aplurality of complex number sequences configured based on a plurality ofconceivable embedding sequences so as to obtain corresponding complexcorrelation values 1512.

In addition, in the case when the embedding sequence in the digitalwatermark embedding apparatus 100 is configured by a plurality ofsymbols or a plurality of bits like the case in (example 3) or (example4) in the embedding sequence generation unit 111, for example, complexcorrelation may be calculated for a complex number sequence configuredbased on the embedding sequence corresponding to a part of the symbolsor bits. That is, it corresponds to performing synchronization using apart of the plurality of symbols or bits.

Operation of the complex correlation value calculation unit 322 is thesame as operation of the complex correlation value calculation unit 226in the digital watermark detection apparatus 200 of the fourthembodiment.

Step 1503) The absolute value calculation unit 323 calculates absolutevalues 1513 of the complex correlation values 1512 obtained by thecomplex correlation value calculation unit 322.

Operation of the absolute value calculation unit 323 is the same asoperation of the absolute value calculation unit 227 in the digitalwatermark detection apparatus 200 of the fourth embodiment.

Step 1504) The synchronization detection maximum value determinationunit 324 finds one having the maximum absolute value 1513 obtained bythe absolute value calculation unit 323 to determine a complexcorrelation value 1512 corresponding to the maximum absolute value 1513.

By the way, depending on a configuration method of the embeddingsequence in the digital watermark embedding apparatus 100, determinationmay be performed using other methods instead of the maximum valuedetermination by the synchronization detection maximum valuedetermination unit 324.

Details of operation of the synchronization detection maximum valuedetermination unit 324 are described later. Other methods that arealternative for the synchronization detection maximum valuedetermination unit 324 are the same as those in the case of the maximumvalue determination unit 223 in the digital watermark detectionapparatus 200 in the fourth embodiment.

Step 1505) The phase calculation unit 325 calculates the phase of thecomplex correlation value determined by the synchronization detectionmaximum value determination unit 324 so as to calculate the amount ofdesynchronization 1502 based on it and output the amount ofdesynchronization 1502 to the detection information extraction unit 330.

Details of operation of the phase calculation unit 325 are describedlater.

By the way, when the digital watermark embedding is performed using thedigital watermark embedding apparatus 100 in the third embodiment,Fourier transform process same as the N−1-dimensional Fourier transformunit 225 in the third embodiment becomes necessary before the process ofthe complex detection sequence extraction unit 321.

<Digital Watermark Detection Apparatus—Synchronization DetectionUnit—Synchronization Detection Maximum Value Determination Unit>

Next, details of operation of the synchronization detection maximumvalue determination unit 324 of the synchronization detection unit 320are described.

Although operation of the synchronization detection maximum valuedetermination unit 324 is almost the same as that of the maximum valuedetermination unit 223 of the digital watermark detection apparatus 200in the fourth embodiment, it is different in that a complex correlationvalue by which the absolute value becomes maximum is obtained instead ofobtaining the embedding sequence as a result.

Processes in the synchronization detection maximum value determinationunit 324 are performed according to the following procedure.

1) An absolute value |ρ^((j))| having a maximum value is found fromabsolute values 1513 |ρ⁽¹⁾|, |ρ⁽²⁾| obtained by the absolute valuecalculation unit 323 as follows,|ρ^((max))|=MAX(|ρ⁽¹⁾|,|ρ⁽²⁾, . . . )  (98)in which MAX ( ) is an operation for returning a maximum value.

2) The complex correlation value ρ^((max)) on which |ρ^((max))| is basedis output to the phase calculation unit 325.

In addition, the synchronization detection maximum value determinationunit 324 may determine whether the maximum correlation value |ρ^((j))|exceeds a predetermined threshold to determine that digital watermark isnot embedded when it does not exceed the predetermined threshold.

<Digital Watermark Detection Apparatus—Synchronization DetectionUnit—Phase Calculation Unit>

Next, details of operation of the phase calculation unit 325 of thesynchronization detection unit 320 are described in detail.

Processes in the phase calculation unit 325 are performed according tothe following procedure.

1) An argument Δθ of the complex correlation value ρ^((max)) obtained bythe synchronization detection maximum value determination unit 324 isobtained as follows,Δθ=Arg[ρ^((max))]  (99)in which Arg[ ] is an operation for obtaining argument of a complexnumber.

2) Since Δθ indicates a shift amount of the phase, the amount ofdesynchronization 1502 Δt is obtained as follows and is output.

$\begin{matrix}{{\Delta\; t} = {\frac{\Delta\theta}{2\pi}T}} & (100)\end{matrix}$T indicates a period of the periodic signal.

In the following, the point that Δθ indicates the shift amount of thephase is described.

The complex correlation value is obtained as shown in the followingequation as described in the description on the complex correlationvalue calculation unit 226 in the digital watermark detection apparatus200 in the fourth embodiment.

$\begin{matrix}{\rho \sim {\left( {\sum\limits_{k = 1}^{L^{\prime}}{\xi_{k}}^{2}} \right){\mathbb{e}}^{j\Delta\theta}}} & (101)\end{matrix}$

Therefore, Arg[ρ^((max))]Δθ(102) holds true, and this indicates theshift amount of the phase that is determined depending on the amount ofdesynchronization in the direction of the N-th dimension axis (timedirection, for example) for the embedded signal 923.

By the way, when the embedding sequence in the digital watermarkembedding apparatus 100 is configured and embedded such that the bitvalue of 0/1 is represented based on difference between plus and minusof the embedding sequence like the case shown in (example 2) and(example 4) of the embedding sequence generation unit 111, for example,a case in which a signal having a phase that is shifted by halfwavelength due to desynchronization cannot be distinguished from a casewhere information in which all bit values are reversed is embedded. Thatis, it cannot be determined which is a correct amount ofdesynchronization between the amount of desynchronization Δt obtained inthe above-mentioned way and

${\Delta\; t} - \frac{T}{2}$in which phase is shifted by half wavelength.

In such a case, for example, by configuring the embedding sequence suchthat one bit in the bit values always takes 1 (or 0) as a bit forjudgment, one by which the bit value becomes the correct value may bedetermined to be correct. In addition, the judgment can be madeavailable by performing coding using asymmetric error correcting code.In addition, determination may be performed using a digital watermarksignal different from the digital watermark of the present invention. Inaddition, one value may be provisionally determined as the amount ofdesynchronization, and bit reversal may be corrected according to theabove-mentioned procedure in the process of the detection informationextraction unit 330 a. Correction is not limited to these examples, andit is needless to say that correction may be performed by other method.

In addition, when spreading is performed based on polarity of plus andminus for each bit by using a partial sequence of the embedding sequencelike (example 4) in the embedding sequence generation unit 111, theargument Argλ of the total sum λ of complex correlation values λ^((a))of each bit position calculated by the bit value detection method thatis described in the last part of the fourth embodiment with reference toFIG. 44 is determined to be the amount of desynchronization Δθ, so thatthe amount of desynchronization can be measured more reliably and moreaccurately compared with the case for obtaining the amount ofdesynchronization based on the complex correlation value for each bit.By the way, although this determining method also includes theabove-mentioned uncertainty of bit reversal, the uncertainty can besolved by using one bit in bit values as a flag for determining bitreversal, for example.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit>

Next, details of operation of the detection information extraction unit330 a are described.

FIG. 49 shows a configuration example of the detection informationextraction unit in the fifth embodiment of the present invention.

The detection information extraction unit 330 a has a configuration sameas that of the detection information extraction unit 220 in the firstembodiment, and includes a detection sequence extraction unit 331, acorrelation value calculation unit 332, a maximum value determinationunit 333, and a detection information reconfiguration unit 334, and itis different from the detection information extraction unit 220 of thefirst embodiment only in that it is configured to receive the amount ofdesynchronization 1502.

By the way, in FIG. 49, please note that the configuration is shown suchthat information flows from the bottom to the top to facilitateunderstanding of correspondence to FIG. 45.

The detection information extraction processes by the detectioninformation extraction unit 330 a are the same as the detectioninformation extraction processes by the detection information extractionunit 220 of the first embodiment except for details of operation of thedetection sequence extraction unit 331.

By the way, when digital watermark embedding is performed using thedigital watermark embedding apparatus 100 in the third embodiment,Fourier transform process that is similar to the N−1-dimensional Fouriertransform unit 225 in the third embodiment is necessary before theprocess of the detection sequence extraction unit 331.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—Detection Sequence Extraction Unit>

In the following, details of operation of the detection sequenceextraction unit 331 of the detection information extraction unit 330 aare described.

Processes in the detection sequence extraction unit 331 are performedaccording to the following procedure.

1) N−1-dimensional complex array of the size of M₁×M₂× . . . ×M_(N−1) isconfigured from the detection complex pattern 1501. The method forconfiguring it is the same as the step 801) in the detection sequenceextraction unit 221 in the before mentioned first embodiment.

2) A complex number sequence is obtained by extracting complex numbervalues one by one in sequence from the complex array obtained in 1) andarranging them. That is, when the complex array is represented as A[ρ₁,p₂, . . . , p_(N−1)](p_(n)≧0),

$\begin{matrix}{c_{1} = {A\left\lbrack {0,0,\ldots\mspace{14mu},0} \right\rbrack}} \\{c_{2} = {A\left\lbrack {1,0,\ldots\mspace{14mu},0} \right\rbrack}} \\\vdots\end{matrix}$is obtained.

By the way, assuming the length of the embedding sequence 913 used whenperforming embedding in the digital watermark embedding apparatus 100 isL, L′=L/2.

3) Phase of each element of the complex number sequence obtained in 2)is displaced in a reverse direction based on the input amount ofdesynchronization 1502. That is, assuming that the amount ofdesynchronization 1502 is

$\begin{matrix}{{{\Delta\; t} = {\frac{\Delta\;\theta}{2\;\pi}T}},} & \; \\\begin{matrix}{c_{1}^{\prime} = {c_{1}{\mathbb{e}}^{{- j}\;\Delta\;\theta}}} \\{c_{2}^{\prime} = {c_{2}{\mathbb{e}}^{{- j}\;\Delta\;\theta}}} \\\vdots\end{matrix} & (104)\end{matrix}$is obtained.

4) Complex number values are extracted one by one sequentially from thecomplex number sequence obtained in 3), so as to arrange the real partand the imaginary part of each extracted complex number value byregarding each of the real part and the imaginary part as an individualreal value. That is, when detection sequence 1521 is represented as i″₁,i″₂, i″_(L),i₁ ″=

[c ₁′]i₂ ″ℑ[c ₁′]i₃ ″=

[c ₂′]i₄ ″=ℑ[c ₂′]  (105)is obtained, wherein

, ℑis an operation for extracting the real part and the imaginary part ofthe complex number respectively.

5) The obtained i″₁, i″₂, . . . , i″_(L) are output to the correlationvalue calculation unit 332 as the detection sequence 1521.

In the case when order of the embedding sequence 913 or elements of thecomplex array is permuted in the complex array generation unit 112 ofthe digital embedding apparatus 100, the order is restored like thedetection sequence extraction unit 221 in the first embodiment.

By the way, in the case when digital watermark embedding is performedusing the digital watermark embedding apparatus 100 in the thirdembodiment, complex number values of elements within a range used by thecomplex array generation unit 112 of the digital watermark embeddingapparatus in the third embodiment are extracted and arranged in theabove-mentioned 2).

<Other Configuration Example of Detection Information Extraction Unit>

Without using the maximum value determination unit 333, the detectioninformation extraction unit 330 a may be configured only by thedetection sequence extraction unit 331, the correlation valuecalculation unit 332, and the detection information reconfiguration unit334, so that detection information may be extracted by performing thefollowing processes. Such a configuration example is shown in FIG. 50.

The detection information extraction unit 330 b shown in FIG. 50re-configures detection information using the embedding sequence bywhich the maximum complex correlation value is obtained in thesynchronization detection unit 320, and re-calculates a correlationvalue again for evaluating reliability of the detection informationbased on the amount of synchronization 1502 obtained by thesynchronization detection unit 320. By doing this, digital watermarkdetection can be performed at higher speed.

1) Processes of the detection sequence extraction unit 331 are the sameas the above-mentioned processes.

2) The correlation value calculation unit 332 is different from thecorrelation value calculation unit 222 of the first embodiment. Insteadof calculating correlation values for all conceivable embeddingsequences, the synchronization detection unit 320 stores, in a memory(not shown in the figure), an embedding sequence corresponding to acomplex correlation value determined to have a maximum absolute value inthe process of the synchronization detection maximum value determinationunit 324, so that the correlation value calculation unit 322 calculatesa correlation value only for the embedding sequence.

It is determined whether reliable digital watermark detection has beenperformed based on whether the correlation value is greater than apredetermined threshold.

3) The detection information reconfiguration unit 334 is similar to thedetection information reconfiguration unit 224 of the first embodimentexcept for the point that reconfiguration of the detection informationis performed using the embedding sequence using the above-mentioned 2).

<Characteristics of the Fifth Embodiment>

According to the digital watermark detection apparatus 300 of thepresent embodiment, in detection of digital watermark, even when thesignal of the digital watermark detection target is desynchronized, theamount of desynchronization can be detected using the digital watermarksignal itself.

That is, by utilizing the point that embedding sequence that is spectrumspread in the N−1-dimensional space is commonly affected bydesynchronization in the direction of N-th dimension, digital watermarkdetection in which synchronization can be performed easily and at highspeed can be performed by using the complex correlation value of thespread sequence in the N−1-dimensional space.

For example, in the case of video signals, digital watermark detectionis possible without using a special synchronization method even when aframe for starting detection is shifted in the time direction. This isvery effective in a use situation in which temporal synchronization isdifficult, such as when detecting digital watermark from a video thatwas re-taken using a video camera and the like, and when detectingdigital watermark from a video that is converted to analog data such asa video tape, for example.

When a video displayed on a screen or TV or the like is taken by a videocamera or a camera of a cellular phone and the like, since the framerate for reproduction is not synchronized with the frame rate for videotaking, there is a case in which re-sampling may occur in sub-frames.This indicates a state in which desynchronization occurs in sub-framelevel (interval shorter than one frame) as a result. Even in such asituation, it is possible to measure the phase of the periodic signal intemporal demodulation, and as mentioned above, the amount ofdesynchronization can be detected.

Especially, according to the above-mentioned digital watermark detectionapparatus, efficient and fast digital watermark detection becomespossible since the amount of desynchronization can be detected bycalculation without using a round-robin method in which shifted amountis sequentially examined. In addition, it is not necessary to add aspecial synchronization signal, digital watermark detection of highquality and high detection performance becomes possible without signaldeterioration due to the synchronization signal and withoutdeterioration of detection performance of digital watermark.

[Sixth Embodiment]

<Phase Modulation>

In the following, a digital watermark embedding apparatus of the sixthembodiment of the present invention is described.

The present embodiment shows an example in which, in the digitalwatermark embedding apparatus 100 of the first embodiment, modulationprocess in the temporal modulation unit 130 is performed using a delayof the periodic signal.

Configuration of the digital watermark apparatus of the presentembodiment is similar to that of the digital watermark embeddingapparatus 100 in the first embodiment, and only the temporal modulationunit 130 is different.

By the way, although examples are shown based on the first embodiment inthe present embodiment, configuration of other embodiments may be usedexcept for the configuration of the temporal modulation unit 130. Forexample, the complex pattern generation unit 110 b in the digitalwatermark embedding apparatus of the third embodiment may be used forthe complex pattern generation unit 110.

<Digital Watermark Embedding Apparatus—Temporal Modulation Unit>

FIG. 51 shows a configuration example of the temporal modulation unit inthe sixth embodiment of the present invention.

The temporal modulation unit 130 c shown in the figure includes aperiodic signal generation unit 131 and a modulation unit 136, andreceives the embedding complex pattern 921 and outputs the embeddingpattern 922.

Generation processes of the embedding pattern 922 by the temporalmodulation unit 130 c are performed according to the followingprocedure.

1) The periodic signal generation unit 131 generates a periodic signal.The periodic signal to be generated is similar to the example of theperiodic signal in the periodic signal generation unit 131 of thetemporal modulation unit 130 a in the first embodiment.

2) The modulation unit 136 modulates the periodic signal generated inthe 1) according to the complex number value of the received embeddingcomplex pattern as follows so as to obtain a N-dimensional embeddingpattern 922.

-   -   determine amplitude of the periodic signal according to the        absolute value of the complex number value.    -   delay the periodic signal according to argument of the complex        number value, that is, change phase.

Next, a concrete example of the temporal modulation is described.

Modulation in the modulation unit 136 is performed by performing QAM(quadrature amplitude) modulation on the periodic signal, as a carrierwave, generated by the periodic signal generation unit 131 according tothe complex number value of each position of the N−1-dimensional complexpattern 921 so as to change the periodic signal to the N-dimensionalpattern.

However, the periodic signal that is the carrier is not necessarily asine wave as mentioned before.

In addition, when all values of the embedding complex pattern 921 areconfigured only by real values, the phase of the periodic signal may bechanged according to the real values while the amplitude of the periodicsignal may be made constant.

More particularly, processes are performed as follows.

Now, assuming that the N−1-dimensional complex pattern is represented asP(x₁, x₂, . . . , x_(N−1)). In addition, the real part and the imaginarypart of P are represented as P_(r) and P_(i) respectively, andP(x ₁ , x ₂ , . . . , x _(N−1))=B(x ₁ , x ₂ , . . . , x _(N−1))e ^(jωτ()x ₁ , x ₂ , . . . , x _(N−1))  (106)herein j is the imaginary unit, and ω is the angular velocity of thebasic frequency of the periodic signal.

It is assumed that the periodic signal generation unit 131 generates aperiodic signal f(t).

N-dimensional pattern M is obtained as the following equation bymodulating B and τ with f(t).M(x ₁ , x ₂, . . . , x_(N−1) , t)=B(x ₁ , x ₂, . . . , x_(N−1))f(t-τ(x ₁, x ₂ , . . . , x _(N−1)))  (107)

Different from general QAM modulation, it should be noted that thebaseband signal p changes, instead of time direction, in the directionof N−1 dimension (space direction in the case of video signal, forexample) that is orthogonal to the time direction.

By such temporal modulation, the phase of the N-dimensional embeddingpattern 922 is spread such that the phase is different according to theposition on the N−1 dimensional space, so that the amount of noisecomponent that appears due to the before-embedding signal 912 whendetecting digital watermark becomes smaller.

<Characteristics of Sixth Embodiment>

The digital watermark embedding apparatus of the present embodimentshows a different configuration example of the temporal modulation unit130 a in the digital watermark embedding apparatus of the firstembodiment, and the digital watermark embedding apparatus of the presentembodiment has characteristics the same as those in digital watermark ofthe first embodiment.

Especially, the temporal modulation unit 130 c modulates theN−1-dimensional embedding pattern that is spectrum spread on theN−1-dimensional space using the phase and the absolute value of theperiodic signal in the N-th dimension direction that is orthogonal tothe N−1-dimensional space, so that it has characteristics that thedesynchronization applied in the N-th dimensional direction exertscommon effects on the N−1-dimensional space.

In addition, in the time modulation unit 130 c, by configuring theembedding pattern 922 such that the phase is different in theN−1-dimensional direction (for example, space direction in the case ofvideo signal) that is orthogonal to the time direction, it can beprevented that every value of the embedding pattern becomes less that aminimum video signal quantization value so that a frame to which digitalwatermark embedding is not performed occurs in the case of video signal,for example. In addition, the video signal can be effectively used astransmission route of digital watermark, and robustness can be increasedagainst an attack to aim at a frame having large digital watermarkamplitude and change the frame.

In addition, since the phase of the embedding pattern is spread in theN−1-dimensional space, the size of the noise component that appears dueto the before embedding signal becomes small in the result of thecorrelation calculation. As a result, digital watermark embedding anddetection can be performed more reliably, and in addition, digitalwatermark embedding and detection can be performed with reliabilitysimilar to that in the conventional technique but with less qualitydeterioration.

[Seventh Embodiment]

<Plural Frequency Band Embedding in Time Axis>

In the following, a digital watermark embedding apparatus in the seventhembodiment of the present invention is described.

This embodiment is an example for performing digital watermark embeddingof the digital watermark embedding apparatus 100 of the first embodimenta plurality of times simultaneously to embed embedding information usinglonger spectrum spread sequence.

FIG. 52 shows a configuration example of the digital watermark embeddingapparatus and a digital watermark detection apparatus of the seventhembodiment of the present invention.

<Digital Watermark Embedding Apparatus>

The digital watermark embedding apparatus 500 shown in FIG. 52 includesa complex pattern generation unit 510, a temporal modulation unit 520,and an embedding pattern superimposing unit 530, and the digitalwatermark embedding apparatus 500 receives embedding information 3111and before embedding signal 3112 and outputs an embedded signal 3113.

Digital watermark embedding processes by the digital watermark embeddingapparatus 500 are performed according to the following procedure.

FIG. 53 is a flowchart of operation of the digital watermark embeddingapparatus in the seventh embodiment of the present invention.

Step 1601) The complex pattern generation unit 510 generates a pluralityof embedding complex patterns 3121 based on the received embeddinginformation 3111.

Each embedding complex pattern 3121 is a N−1-dimensional patternconfigured by complex numbers and indicates content of embeddinginformation.

Details of operation of the complex pattern generation unit 510 aredescribed later.

Step 1602) The temporal modulation unit 520 generates the embeddingpattern 3122 based on each embedding complex pattern 3121 generated inthe complex pattern generation unit 510.

The operation of the temporal modulation unit 520 is the same as that inthe first embodiment. However, the periodic signals generated in eachtemporal modulation unit 520 are periodic functions that are orthogonalwith each other. For example, they may be periodic functions each havinga different basic frequency.

In addition, the temporal modulation unit shown in embodiments otherthan the first embodiment may be used as the temporal modulation unit520. For example, the temporal modulation unit of the second embodimentor the sixth embodiment may be used.

When using the temporal modulation unit 130 b of the second embodimentas the temporal modulation unit 520, processes of temporal modulationfor a plurality of frequencies may be performed by one-time Fouriertransform.

Step 1603) The embedding pattern superimposing unit 530 superimposeseach embedding pattern 3122 generated in each temporal modulation unit520 on the received before-embedding signal 3112 to output the embeddedsignal 3113. Details of operation of the embedding pattern superimposingunit 530 are described later.

<Digital Watermark Embedding Apparatus—Complex Pattern Generation Unit>

In the following, details of operation of the complex pattern generationunit 510 are described.

FIG. 54 shows a configuration example of the complex pattern generationunit in the seventh embodiment of the present invention.

The complex pattern generation unit 510 includes an embedding sequencegeneration unit 511 and a plurality of complex array generation units512, and receives the embedding information 3111 and outputs theembedding complex pattern 3121.

Embedding complex pattern generation processes by the complex patterngeneration unit 510 are performed according to the following procedure.

FIG. 55 is a flowchart of operation of the complex pattern generationunit in the seventh embodiment of the present invention.

Step 1701) The embedding sequence generation unit 511 generates asequence of numbers representing embedding information based on thereceived embedding information 3111, and divides the sequence togenerate a plurality of embedding sequences 3211.

Details of operation of the embedding sequence generation unit 511 aredescribed later.

Step 1702) The complex array generation unit 512 assigns each embeddingsequence 3213 generated by the embedding sequence generation unit 511 tothe real part and the imaginary part of elements of the N−1-dimensionalcomplex array to generate the embedding complex pattern 3121.

Operation of each complex array generation unit 512 is the same as thatof the complex array generation unit 112 in the first embodiment.

In addition, the complex pattern generation unit 510 may be configuredbased on the complex pattern generation unit 110 b in the thirdembodiment. That is, the pattern obtained by the complex arraygeneration unit 512 may be further Fourier transformed by a processsimilar to the N−1-dimensional inverse Fourier transform unit 113 of thethird embodiment so as to regard the result as the embedding complexpattern 3121.

<Digital Watermark Embedding Apparatus—Complex Pattern GenerationUnit—Embedding Sequence Generation Unit>

After generating the embedding sequence by a procedure similar to thatin the embedding sequence generation unit 111 in the first embodiment,the embedding sequence generation unit 511 divides the embeddingsequence into a plurality of parts. For example, when a sequence w={w₁,w₂, . . . , w_(nL)} is generated by a procedure similar to that in theembedding sequence generation unit 111, for example, each of theembedding sequences w^([1]), w^([2]), . . . , w^([n]) is generated as

$\begin{matrix}{\quad\begin{matrix}\begin{matrix}\begin{matrix}{w^{\lbrack 1\rbrack} = \left\{ {w_{1},w_{2},\cdots\mspace{14mu},w_{L}} \right\}} \\{w^{\lbrack 2\rbrack} = \left\{ {w_{L + 1},w_{L + 2},\cdots\mspace{14mu},w_{2L}} \right\}}\end{matrix} \\\vdots\end{matrix} \\{w^{\lbrack N\rbrack} = \left\{ {w_{{{({n - 1})}L} + 1},w_{{{({n - 1})}L} + 2},\cdots\mspace{14mu},w_{nL}} \right\}}\end{matrix}} & (108)\end{matrix}$wherein n is a total number of divisions.

By the way, although an example is shown in which the embedding sequenceis divided in sequence by a predetermined number from the top, thesequence may be divided by any method as long as it is divided by apredetermined dividing method. For example,

$\quad\begin{matrix}\begin{matrix}\begin{matrix}\begin{matrix}{w^{\lbrack 1\rbrack} = \left\{ {w_{1},w_{n + 1},\cdots\mspace{14mu},w_{{{({L - 1})}n} + 1}} \right\}} \\{w^{\lbrack 2\rbrack} = \left\{ {w_{2},w_{n + 2},\cdots\mspace{14mu},w_{{{({L - 1})}n} + 2}} \right\}}\end{matrix} \\\vdots\end{matrix} \\{w^{\lbrack n\rbrack} = \left\{ {w_{n},w_{2n},\cdots\mspace{14mu},w_{nL}} \right\}}\end{matrix} & (109)\end{matrix}$may be adopted.

<Digital Watermark Embedding Apparatus—Embedding Pattern SuperimposingUnit>

In the following, details of operation of the embedding patternsuperimposing unit 530 are described.

Operation of the embedding pattern superimposing unit 530 is almost thesame as that of the embedding pattern superimposing unit 140 in thefirst embodiment. But, only the following point is different.

The embedding pattern superimposing unit 530 adds, to superimpose, eachN-dimensional embedding pattern 3122 generated in each temporalmodulation unit 520 to the N-dimensional signal that is received as thebefore-embedding signal 3112, and outputs the N-dimensional signal thatis the result of superimposing as the embedded signal 3113. In thisprocess, all of the plurality of embedding patterns 3122 are added andsuperimposed. In addition, each embedding pattern 3122 may be enhancedby different embedding strength for superimposing. For example, in thecase when deterioration characteristics with respect to frequency bandare different for each embedding pattern 3122 for embedding, differentembedding strength may be used for each embedding pattern such thatdetection for each embedding pattern can be performed with sameaccuracy.

<Digital Watermark Detection Apparatus>

The digital watermark detection apparatus 600 in the present embodimentincludes a plurality of synchronization detection units 620, and adetection information extraction unit 630, and the digital watermarkdetection apparatus 600 receives the embedded signal 3113 and outputsthe detection information 3114.

Digital watermark detection processes by the digital watermark detectionapparatus 600 are performed according to the following procedure.

FIG. 56 is a flowchart of operation of the digital watermark detectionapparatus in the seventh embodiment of the present invention.

Step 1801) Each temporal demodulation unit 610 performs demodulation inthe time axis direction to obtain the detection complex pattern 3161.Although content of processes in each temporal demodulation unit 610 issimilar to that in the temporal demodulation unit 210 in the digitalwatermark detection apparatus 200 in the first embodiment, each of theperiodic functions used in the temporal modulation units 520 of thedigital watermark embedding apparatus 500 is used for each temporaldemodulation unit 610.

By the way, like the digital watermark detection apparatus 200 of thefirst embodiment, pre-processing may be performed on the embedded signal3113 before performing temporal demodulation process by the temporaldemodulation unit 610.

In addition, the temporal demodulation unit shown in embodiments otherthan the first embodiment can be used as the temporal demodulation unit610. For example, the temporal demodulation unit 210 c in the secondembodiment may be used.

When using the temporal demodulation unit 210 c in the second embodimentas the temporal demodulation unit 610, processes of temporaldemodulation for a plurality of frequencies may be performed by one-timeFourier transform.

Step 1802) Each synchronization detection unit 620 detects the amount ofdesynchronization, in a time axis (N-th dimension axis) direction, thatwas applied beforehand to the embedded signal 3113 from each detectioncomplex pattern 3161 obtained by each the temporal demodulation unit610, and outputs it as the amount of desynchronization 3162.

Operation of the synchronization detection unit 620 is the same as thatof the synchronization detection unit 320 of the digital watermarkdetection apparatus 300 in the fifth embodiment.

Step 1803) The detection information extraction unit 630 extractsdigital watermark information embedded by the digital watermarkembedding apparatus 500 based on each amount of desynchronization 3162obtained by the temporal demodulation units 610, and outputs the digitalwatermark information as the detection information 3114.

Details of operation of the detection information extraction unit 630are described later.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit>

In the following, details of operation of the detection informationextraction unit are described.

FIG. 57 shows configuration of the detection information extraction unitin the seventh embodiment of the present invention.

The detection information extraction unit 630 shown in the figure issimilar to that of the detection information extraction unit 330 of thefifth embodiment, but it is different in that the detection sequenceextraction unit 631 is provided for each received detection complexpattern 3161 and each amount of desynchronization 3162.

By the way, in FIG. 57, please note that the configuration is shown suchthat information flows from the bottom to the top to facilitateunderstanding of correspondence to FIG. 54.

The detection information extraction process by the detectioninformation extraction unit 630 is similar to the detection informationextraction process in the detection information extraction unit 330 inthe fifth embodiment except for a point that each of a plurality ofdetection sequence extraction unit 631 extracts the detection sequence3313 based on the received detection complex pattern 3161 and the amountof desynchronization 3162 and for details of operation of thecorrelation value calculation unit 632.

In addition, like the other configuration example of the detectioninformation extraction unit 330 described in the fifth embodiment,without using the maximum value determination unit 633, the detectioninformation may be re-configured using the detection information bywhich maximum complex correlation value is obtained in thesynchronization detection unit 320, and, in addition to that,correlation value for evaluating the reliability of the detectioninformation may be calculated again based on the amount ofdesynchronization obtained by the synchronization detection unit 320.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit—Correlation Value Calculation Unit>

In the following, operation of the correlation value calculation unit632 is described in detail.

Processes in the correlation value calculation unit 632 are performedaccording to the following procedure.

1) The detection sequences 3313 i″^([1]), i″^([2]), . . . each obtainedby the detection sequence extraction unit 631 are integrated so as toobtain the sequence i″ as follows,

wheni″^([k])={i₁″^([k]), i₂″[k], . . . , i_(L)″^([k])}i″={i₁″^([1]), i₂″^([1]), . . . , i_(L)″^([1]), i₁″^([2]), i₂″^([2]), .. . , i_(L)″^([2]), . . . i₁″^([n]), i₂″^([n]), . . . ,i_(L)″^([n])}  (110)wherein [k] described on the shoulder of i″ represents that i″ is adetection sequence obtained from a k-th detection complex pattern 3161by the k-th detection sequence extraction unit 631. In the equation, nindicates a total number of the received detection complex patterns3161. By the way, although an example is shown in which each detectionsequence is simply concatenated here, the sequences may be connected byextracting values from each detection sequence in predetermined order aslong as it corresponds to the method for dividing embedding sequence inthe embedding sequence generation unit 511 of the digital watermarkembedding apparatus 500. For example, they may connected as follows.i″={i₁″^([1]), i₁″^([2]), . . . , i₁″^([n]), i₂″^([1]), i₁″^([2]), . . ., i₂″^([n]), . . . , i_(L)″^([2]), i_(L)″^([2]), . . . ,i_(L)″[n]}  (111)

2) the correlation value 3314 is obtained based on the sequence i″obtained in the above-mentioned 1) by performing processes similar tothose of the correlation value calculation unit 332 of the digitalwatermark detection apparatus 300 of the fifth embodiment. But, itshould be noted that the conceivable embedding sequence that is thesubject for correlation calculation is a sequence w={w₁, w₂, . . . ,w_(nL)} that is generated in the embedding sequence generation unit 511of the digital watermark embedding apparatus 500 and that is one beforebeing divided.

<Improvement of Accuracy by Integrating the Amounts ofDesynchronization>

The synchronization detection unit 620 May obtain the amount ofdesynchronization with higher accuracy according to the followingprocedure based on the amount of desynchronization 3162 obtained foreach detection complex pattern 3161.

1) Assuming that each amount of desynchronization is

${{\Delta\; t_{i}} = {\frac{\Delta\;\theta_{1}}{2\;\pi}T_{1}}},{{\Delta\; t_{2}} = {\frac{\Delta\;\theta_{2}}{2\;\pi}T_{2}}},\cdots$wherein T₁, T₂, . . . are periods of the periodic signal of eachtemporal demodulation unit 610.

2) A maximum one is selected from Δt₁, Δt₂, . . . as Δt_(max).Alternatively, Δt_(i) corresponding to a periodic signal having themaximum period may be selected.

3) A following equation is considered based on Δt_(i), T_(i), Δt_(max)for each i to obtain n_(i).Δt _(i) +n _(i) T _(i) =Δt _(max)  (112)

4) Assuming that each integer value closest to each n_(i) is n′_(i).

5) Following Δt′_(i) is obtained using n′₁.Δt _(i) ′=Δt _(i) +n _(i) ′T _(i)  (113)

This means obtaining a shift amount, as Δt'_(i), in the N-th dimensionaxis direction at the position of the n′_(i)-th period according to theposition of Δt_(max) for each periodic signal.

FIG. 58 shows a manner of the above-mentioned calculation using the twoperiodic signals. In the figure, Δθ₁=5π/3 is obtained for the periodicsignal 1 of a period 6, and Δθ₂=π/2 is obtained for the periodic signal2 of a period 4, and they are shown as white circles. In this case,Δt₁=5, Δt₂=1. In addition, the positions of Δt₂+T₂ and Δt₂+2T₂ are shownby black circles. Δt₁ is selected as Δt_(max) so that n′₂=1 is obtainedby the above procedures 3) and 4). This indicates that points of thephases Δθ₁ and Δθ₂ of the two periodic signal overlap with each other atthe position of the left side black circle among the two black circles.As a result, Δt′₂=Δt₂+n′₂T₂=5 is obtained.

By the way, as to i corresponding to the periodic signal selected asΔt_(max), n′_(i)=1 holds true.

6) An average value of Δt′_(i) obtained in the above-mentioned way isobtained so as to regard it as the shift amount Δt for the whole asfollows.

$\begin{matrix}{{\Delta\; t} = {\frac{1}{k}{\sum\limits_{i = 1}^{k}{\Delta\; t_{i}^{\prime}}}}} & (114)\end{matrix}$In the equation, k indicates a number of periodic signals.

In the example of FIG. 58, an example of a case in which there is noerror in detection of each amount of desynchronization is shown. But,when there is an error in detection of each amount of desynchronization,there is a possibility in that n_(i) does not become an integer. Byobtaining n′_(i) as an integer in the above-mentioned procedure 4) andby finally obtaining the average of Δt′_(i), maximum likelihood value ofthe amount of desynchronization on the N-th dimension axis is obtainedin consideration of an error.

In addition, when obtaining the average value of Δt′_(i), a shift amountthat is obviously position-displaced may be disregarded, for example.According to this method, for example, a case in which an attack isapplied to a frequency corresponding to a specific frequency signal sothat detection of the amount of desynchronization obtained from adetection complex pattern 3161 is failed can be removed.

7) Since Δt is a value of the shift amount in the N-th dimensiondirection that is actually obtained accurately, the amount ofdesynchronization of each frequency signal

${\Delta\;{\overset{\sim}{t}}_{i}} = {\frac{\Delta\;{\overset{\sim}{\theta}}_{i}}{2\;\pi}T_{i}}$is re-obtained from this as follows.

$\begin{matrix}{{\Delta\;{\overset{\sim}{t}}_{l}} = \begin{matrix}{{\Delta\; t} - {n_{I}^{\prime}T_{I}}} & \left( {{{When}\mspace{14mu}\Delta\; t} \geq {n_{I}^{\prime}T_{I}}} \right) \\{{\Delta\; t} - {\left( {n_{I}^{\prime} - 1} \right)T_{I}}} & \left( {{{When}\mspace{14mu}\Delta\; t} < {n_{I}^{\prime}T_{I}}} \right)\end{matrix}} & (115)\end{matrix}$

By obtaining the shift amount in the N-th dimension direction accuratelybased on the amount of desynchronization 3162 obtained for eachdetection complex pattern 3161 in the above-mentioned way, and byre-obtaining the amount of desynchronization using this, it becomespossible to calculate a more accurate amount of desynchronization. As aresult, detection accuracy of the digital watermark can be improved.

<Characteristics of Seventh Embodiment>

According to the digital watermark embedding apparatus and the digitalwatermark detection apparatus of the present embodiment, embeddinginformation of a longer information length can be embedded as digitalwatermark by using a plurality of frequency bands.

In addition, by finally calculating a correlation value as a whole fordetection sequences that are results of performing synchronizationindividually and separately so as to evaluate reliability of detection,reliability of the whole detection result can be made clear moreaccurately compared with the case in which digital watermark is embeddedand detected individually and separately.

In addition, the spectrum spread sequence length can be increased, sothat digital watermark can be embedded with higher reliability. This isdescribed as follows.

According to the before-mentioned document—Susumu Yamamoto, TakaoNakamura, Youichi Takashima, Atsushi Katayama, Ryo Kitahara, TakashiMiyatake, “Consideration on evaluation of detectability for frame-basedvideo watermarking”, Forum on information technology, FIT2005, J-029,2005—, in the case of digital watermarking using spectrum spreading andcorrelation calculation, the detection evaluation value indicatingreliability of detection in the sense of false positive of digitalwatermark increases in proportion to the square root of the sequencelength of the spectrum spreading. On the other hand, when digitalwatermark is embedded by superimposing it on a plurality of frequencybands like the present embodiment, it is necessary to decrease energy ofwatermark signal for each frequency band for suppressing the wholesignal deterioration. That is, when performing multiplexing on nfrequency bands without changing the degree of signal deterioration (forexample, without changing the value of PSNR), the energy of eachwatermark signal becomes 1/n and the amplitude becomes 1/√n comparedwith the case when embedding on a single frequency band. This equals tothat individual embedding strength becomes 1/√n.

According to the before-mentioned document—Susumu Yamamoto, TakaoNakamura, Youichi Takashima, Atsushi Katayama, Ryo Kitahara, TakashiMiyatake, “Consideration on evaluation of detectability for frame-basedvideo watermarking”, Forum on information technology, FIT2005, J-029,2005—, when the embedding strength becomes 1/√n, if the original imagecomponent that becomes noise for watermark is small enough, thedetection evaluation value of the digital watermark becomes constantirrespective of embedding strength (in FIG. 1 in the document, when abecomes a maximum limit, that is, when the embedding strength becomeslarge enough compared with the original image component, E[ρ]asymptotically comes closer to √1). In addition, when the original imagecomponent that becomes noise for watermark is large enough, detectionevaluation value of digital watermark becomes 1/√n (in FIG. 1 in thedocument, when a becomes a minimum limit, that is, when the embeddingstrength becomes small enough compared with the original imagecomponent, E[ρ] comes closer to a straight line that passes though theorigin point).

As a result, compared with the case in which watermark is embedded in asingle frequency band, when performing multiplexing onto n frequencybands,

-   -   if the original image component that becomes noise for watermark        is small enough, the detection evaluation value of the digital        watermark becomes large in proportion to the square root of        sequence length of spectrum spreading,    -   even when the original component image that becomes noise for        watermark is large enough, detection evaluation value of digital        watermark does not change at worst,        so that the detection evaluation value becomes large as a whole,        and as a result, detection of higher reliability becomes        possible.

In addition, by using the method for obtaining the shift amount in theN-th dimension direction accurately based on the amount ofdesynchronization 3162 obtained for each detection complex pattern 3161to re-obtain, using this, the amount of desynchronization, the amount ofdesynchronization can be obtained more accurately, and detectionaccuracy of digital watermark can be improved, and reversely, embeddingstrength of digital watermark can be made week for the same level ofdetection accuracy, so that digital watermark of small qualitydeterioration can be realized.

In addition, when using the temporal modulation unit 130 b and thetemporal demodulation units 210 c and 210 d as the temporal modulationunit 520 and the temporal demodulation unit 610, processes of temporalmodulation and temporal demodulation for a plurality of frequencies canbe performed by one-time Fourier transform, so that processes can beperformed at higher speeds.

[Eighth Embodiment]

<Time Multiplexing Embedding>

In the following, a digital watermark embedding apparatus and a digitalwatermark detection apparatus of the eighth embodiment of the presentinvention are described.

This embodiment is an example for using the digital watermark embeddingapparatus and the digital watermark detection apparatus of the fifthembodiment to embed, into a before-input signal, a synchronizationpattern and a following embedding pattern that is based on a pluralityof pieces of embedding information and detect the amount ofdesynchronization so as to perform embedding and detection efficientlyfor large amount of embedding information.

<Digital Watermark Embedding Apparatus>

The digital watermark embedding apparatus of the present embodiment hasa configuration similar to that of the digital watermark embeddingapparatus 100 of the first embodiment, but a part of operation of thecomplex pattern generation unit 110 is different.

Embedding processes of digital watermark by the digital watermarkembedding apparatus 100 of the present embodiment are performedaccording to the following procedure.

FIG. 59 is a flowchart showing operation of the digital watermarkembedding apparatus in the eighth embodiment of the present invention.

Step 1901) The complex pattern generation unit 110 generates anembedding complex pattern 921 based on the received embeddinginformation 911. In this process, the embedding complex pattern 921 isgenerated such that the embedding complex pattern 921 changes based onembedding information for each one period of the periodic signalgenerated by the periodic signal generation unit 131 of the temporalmodulation unit 130.

Details of operation of the complex pattern generation unit 110 aredescribed later.

Step 1902) The temporal modulation unit 130 generates an embeddingpattern 922 based on the complex pattern 921 that is generated by thecomplex pattern generation unit 110 and that is stored in the firststorage 150 to store the embedding pattern 922 into the second storage160.

Operation of the temporal modulation unit 130 is the same as that of thetemporal modulation unit 130 in the first embodiment except for a pointthat the embedding pattern 922 changes for each period according to theembedding complex pattern 921 generated by the complex patterngeneration unit 110.

By the way, as to the temporal modulation unit 130, temporal modulationunits of other embodiments may be used. For example, the temporalmodulation unit 130 b of the second embodiment may be used, and thetemporal modulation unit 130 c of the sixth embodiment may be used, forexample.

Step 1903) The embedding pattern superimposing unit 140 superimposes, onthe received before-embedding signal 912, the embedding pattern 922 thatis generated by the temporal modulation unit 130 and that is stored inthe second storage unit 160 to output the embedded signal 923.

Operation of the embedding pattern superimposing unit 140 is the same asthat of the first embodiment.

<Digital Watermark Embedding Apparatus—Complex Pattern Generation Unit>

In the following, derails of operation of the complex pattern generationunit 110 c are described.

FIG. 60 shows a configuration example of the complex pattern generationunit in the eighth embodiment of the present invention.

The complex pattern generation unit 110 c includes an embedding sequencegeneration unit 117, a complex array generation unit 116, an embeddinginformation dividing unit 114, and a synchronization sequence generationunit 115, and the complex pattern generation unit 110 c receives theembedding information 911 and outputs the embedding complex pattern 921.

Embedding complex pattern generation processes by the complex patterngeneration unit 110 c are performed according to the followingprocedure.

FIG. 61 is a flowchart of operation of the complex pattern generationunit in the eighth embodiment of the present invention.

Step 2001) The synchronization sequence generation unit 115 generates asynchronization sequence 917 that is a predetermined sequence of numbersfor synchronization.

Details of operation of the synchronization sequence generation unit 115are described later.

Step 2002) The embedding information dividing unit 114 divides thereceived embedding information 911 into a plurality of pieces of partialembedding information 916. Any method can be used for the division. Forexample, the embedding information 911 may be divided by k bits insequence from the top.

Step 2003) The embedding sequence generation unit 117 generates theembedding sequence 913 that is a sequence of numbers representingembedding information.

Operation of the embedding sequence generation unit 117 is the same asthat of the embedding sequence generation unit 111 of the firstembodiment except for a point that the embedding sequence 913 isgenerated for each of the plurality of pieces of partial embeddinginformation 916.

Step 2004) The complex array generation unit 116 assigns each of thesynchronization sequence 917 generated by the synchronization sequencegeneration unit 115 and each embedding sequence 913 generated by theembedding sequence generation unit 117 into the real part and theimaginary part of elements on the N−1-dimensional complex array.

Details of operation of the complex array generation unit 116 aredescribed later.

<Digital Watermark Embedding Apparatus—Complex Pattern GenerationUnit—Synchronization Sequence Generation Unit>

The synchronization sequence generation unit 115 generates thesynchronization sequence 115 by the following processes.

The synchronization sequence 115 is a sequence of values used forsynchronization in the digital watermark detection apparatus and isgenerated using a pseudo-random number sequence such that thesynchronization sequence does not overlap with other embedding sequence.That is, assuming that the pseudo-random number sequence is SPN={SPN₁,SPN₂, . . . , SPN_(L)} (L is a length of the sequence), thesynchronization sequence s={s₁, s₂, . . . , s_(L)} may be determined asfollows.s=SPN={SPN₁, SPN₂, . . . , SPN_(L)}  (116)

<Digital Watermark Embedding Apparatus—Complex Pattern GenerationUnit—Complex Array Generation Unit>

Operation of the complex array generation unit 116 is similar to that ofthe complex array generation unit 112 in the digital watermark embeddingapparatus of the first embodiment, but it is different in that thecomplex array generation unit 116 configures complex arrays for each ofthe synchronization sequence 917 and the plurality of embeddingsequences 913 and generates the complex arrays such that the embeddingcomplex pattern 921 is successively switched for each one period of theperiodic signal generated by the periodic signal generation unit 131 ofthe temporal modulation unit 130.

The complex array generation unit 116 generates the embedding complexpattern 921 by the following processes.

1) By a procedure similar to that of the complex array generation unit112 in the digital watermark embedding apparatus 100 of the firstembodiment, an embedding complex pattern SP based on the synchronizationsequence 917 generated by the synchronization sequence generation unit115 is generated.

2) By a procedure similar to that of the complex array generation unit112 in the digital watermark embedding apparatus 100 in the firstembodiment, the embedding complex pattern A₁, A₂, . . . , A_(k) isgenerated based on each embedding sequence 913 generated by theembedding sequence generation unit 117, in which k indicates a number ofembedding sequences 913 generated in the embedding sequence generationunit 117, that is, k is a number of divisions of information in theinformation dividing unit 114.

3) For each one period of the periodic signal generated by the periodicsignal generation unit 131 of the temporal modulation unit 130, theembedding complex pattern is output repeatedly in the followingsequence.SP,SP,A₁, A₂, . . . , A_(k), SP, SP, A₁, A₂, . . . , A_(k),  (117)

The . . . at the end indicates that the whole is similarly repeated.

In this example, although the embedding complex pattern SP based on thesynchronization sequence 917 is repeated two times and output, it may berepeated equal to or more than three times. In such a case, it isneedless to say that digital watermark detection is performed in thedigital watermark detection apparatus assuming that it is repeated aplurality of times.

The embedding pattern is generated based on the embedding complexpattern 921 generated in the above-mentioned way, and the pattern issuperimposed on the before-embedding signal, so that the embeddinginformation is embedded in a time division manner.

FIG. 62 shows an example for embedding a plurality of pieces ofinformation continuously in a time division manner. As shown in thefigure, embedding patterns generated from each embedding complex patternare connected so as to be superimposed on the before-embedding signal.

<Digital Watermark Detection Apparatus>

FIG. 63 shows a configuration example of the digital watermark detectionapparatus in the eighth embodiment of the present invention.

The digital watermark detection apparatus 700 shown in the figureincludes an embedded signal dividing unit 710, a synchronizationtemporal demodulation unit 720, a synchronization detection unit 730, asynchronized signal dividing unit 740, a temporal demodulation unit 750,a detection information extraction unit 760, and a pattern storage 770,and the digital watermark detection apparatus 700 receives the embeddedsignal 923 and outputs detection information 3812.

By the way, in FIG. 63, please note that the configuration is shown suchthat information flows from the bottom to the top to facilitateunderstanding of correspondence to FIG. 10.

Digital watermark detection processes by the digital watermark detectionapparatus 700 are performed according to the following procedure.

FIG. 64 is a flowchart of operation of the digital watermark detectionapparatus in the eighth embodiment of the present invention.

Step 2101) A portion of the embedded signal 923 of a length same as theperiod of the periodic signal in the temporal modulation unit 130 of thedigital watermark embedding apparatus 100 is supplied to the embeddedsignal dividing unit 710 so as to obtain a partial embedded signal 3816.

Step 2102) The synchronization temporal demodulation unit 720 performsdemodulation on the partial embedded signal 3816 divided in step 2101 bya procedure similar to that of the temporal demodulation unit 210 of thedigital watermark detection apparatus in the first embodiment to obtaina complex pattern as the synchronization complex pattern 3813.

By the way, the synchronization temporal demodulation unit 720 may beconfigured to operate similarly to the temporal demodulation unit inother embodiments of the present invention. For example, it may operatesimilarly to the temporal demodulation unit 210 c of the secondembodiment.

Step 2103) The synchronization detection unit 730 obtains the amount ofdesynchronization 3814 for the synchronization complex pattern 3813 thatis obtained in step 2102 by a procedure similar to the synchronizationdetection unit 320 of the digital watermark detection apparatus 300 inthe fifth embodiment.

If the amount of desynchronization cannot be obtained in thesynchronization detection unit 730, the process returns to step 2101 sothat processes are repeated for an embedded signal one period after.

Details of operation of the synchronization detection unit 730 aredescribed later.

Step 2104) The synchronized signal dividing unit 740 divides theembedded signal 923, from a position shifted by the amount ofdesynchronization 3814 obtained in step 2103, by a length the same asthe period of the periodic signal in the temporal modulation unit 130 ofthe digital watermark embedding apparatus 100, so as to obtainsynchronized partial signals 3817 the number of which is the same as thenumber of the pieces of the embedding information divided by theembedding information dividing unit 114 of the digital watermarkembedding apparatus 100.

Details of operation of the synchronized signal dividing unit 740 aredescribed later.

Step 2105) The temporal demodulation unit 750 demodulates each of thesynchronized partial signals 3817 divided in step 2104 into a complexpattern by a procedure similar to the temporal demodulation unit 210 ofthe digital watermark detection apparatus 200 in the first embodiment,and the complex pattern is stored in the pattern storage unit 770 as adetection complex pattern 3815.

By the way, the temporal demodulation unit 750 may be configured tooperate similarly to the temporal demodulation unit in other embodimentsof the present invention. For example, it may be configured to operatesimilarly to the temporal demodulation unit 210 c of the secondembodiment.

Step 2106) The detection information extraction unit 760 obtainsdetection information for each of the detection complex patterns 3815obtained in step 2105 by a procedure similar to the detectioninformation extraction unit 220 of the digital watermark detectionapparatus 200 in the first embodiment, and in addition to that, thedetection information extraction unit 760 connects each detectioninformation to output the whole detection information 3812.

Details of operation of the detection information extraction unit 760are described later.

<Digital Watermark Detection Apparatus—Synchronization Detection Unit>

In the following, details of operation of the synchronization detectionunit 730 are described.

Operation of the synchronization detection unit 730 is similar to thatof the synchronization detection unit 320 of the digital watermarkdetection apparatus 300 in the fifth embodiment, but, it is different inthe following point.

The complex correlation value calculation unit 322 in the fifthembodiment calculates complex correlation for the complex numbersequence configured based on the assumed embedding sequence. Incontrast, the complex correlation value calculation unit 322 in thepresent embodiment calculates complex correlation for complex numbersequence configured based on the synchronization sequence 917 generatedby the synchronization sequence generation unit 115 of the digitalwatermark embedding apparatus 110 c.

In addition, when the value of the absolute value 1513 does not exceed apredetermined threshold, the synchronization detection maximum valuedetermination unit 324 determines that the synchronization could not bedetected so that it does not output the amount of desynchronization1502.

As mentioned before, processes are performed repeatedly, until theamount of desynchronization 3814 is obtained, on the embedded signalthat is successively cut out by a length of one period in the embeddedsignal dividing unit 710, so that the embedded signal is successivelyscanned until the synchronization sequence is found.

In this case, as shown in FIG. 62, the embedding pattern(“synchronization pattern” in FIG. 62) configured from thesynchronization sequence is repeated twice. Thus, even though theprocess is started from any timing that is not synchronized beforehand,only by performing the process period by period, a cyclically shiftedsynchronization pattern of one period is found sooner or later, so thata synchronization pattern can be detected.

For example, in the case of video signal and the like, it is notnecessary to search for a synchronization pattern while shifting frameby frame. Thus, the process can be performed on a period by periodbasis, search for the synchronization pattern can be performedefficiently.

This manner is shown in FIG. 65.

<Digital Watermark Detection Apparatus—Synchronized Signal DividingUnit>

In the following, details of operation of the synchronized signaldividing unit 740 are described.

The synchronized signal dividing unit 740 divides the embedded signal923 by one period from a synchronized position based on the amount ofdesynchronization 3814 obtained by the synchronization detection unit730. That is, the synchronized signal dividing unit 740 performsdividing by skipping the embedded signal 923 by the amount ofdesynchronization 3814

${\Delta\; t} = \frac{T\;\Delta\;\theta}{2\;\pi}$or going back by T-Δt on the embedded signal 923, so that it can be cutout by one period while being synchronized with the embedding pattern.

By the way, depending on detection timing of the synchronizationpattern, there may be a case in which a top synchronized partial signal3817 divided by the synchronized signal dividing unit 740 is a sectionwhere the synchronization sequence is embedded, and a case in which thetop synchronized partial signal 3817 is a section where a firstembedding sequence is embedded. This can be easily determined by trying,again, detection of synchronization sequence or corresponding embeddingsequence for each section.

By doing this, each section corresponding to each embedding sequence iscut out as the synchronized partial signal 3817.

<Digital Watermark Detection Apparatus—Detection Information ExtractionUnit>

In the following, a configuration example of the detection informationextraction unit 760 is shown.

FIG. 66 is a configuration example of the detection informationextraction unit in the eighth embodiment of the present invention.

The detection information extraction unit 760 includes a detectionsequence extraction unit 761, a correlation value calculation unit 762,a maximum value determination unit 763, a detection informationre-configuration unit 764, and a detection information connecting unit765, and the detection information extraction unit 760 receives thedetection complex pattern 3815 and outputs the detection information3812.

By the way, in FIG. 66, please note that the configuration is shown suchthat information flows from the bottom to the top to facilitateunderstanding of correspondence to FIG. 60.

Detection information extraction processes by the detection informationextraction unit 760 are performed by the following procedure.

FIG. 67 is a flowchart of operation of the detection informationextraction unit in the eighth embodiment of the present invention.

Step 2201) In each of the detection sequence extraction unit 761, thecorrelation value calculation unit 762, the maximum value determinationunit 763 and the detection information re-configuration unit 764, thepartial detection information 3615 is obtained by performing processessimilar to operation of each corresponding unit of the detectioninformation extraction unit 220 in the digital watermark detectionapparatus 200 of the first embodiment.

But, they are different in that processes are performed for each ofinput detection complex pattern 3815, and the detection informationre-configuration unit 764 outputs a plurality of pieces of partialdetection information 3615.

Step 2202) The detection information connecting unit 765 connects theplurality of pieces of partial detection information 3615 obtained bythe detection information re-configuration unit 764 so as to configureand output the detection information 3812.

Connecting of the plurality of pieces of partial detection information3615 is a reverse process of dividing process in the embeddinginformation dividing unit 114 of the digital watermark embeddingapparatus. For example, when it is divided into groups of K bits insequence from the front part of the embedding information 911 in theembedding information dividing unit 114, the pieces of partial detectioninformation may be connected in sequence.

<Other Configuration Example of the Digital Watermark DetectionApparatus>

In the above example, although an example is shown in which thesynchronized signal dividing unit 740 divides the embedded informationby a length of one period, when the complex array generation unit 116 ofthe digital watermark embedding apparatus 100 embeds the embeddingcomplex pattern corresponding to the synchronization sequence such thatit repeats equal to or more than four times, the synchronized signaldividing unit 740 may divides the embedded signal by a length of aplurality of periods.

In the above example, although an example is shown in which the embeddedsignal dividing unit 710 divides the embedded signal 923 by one period,the embedded signal dividing unit 710 may divide the embedded signal bya length of a plurality of periods after determining a head position inthe repetition when the complex array generation unit 116 of the digitalwatermark embedding apparatus 100 generates the embedding complexpatterns corresponding to each embedding sequence such that theembedding complex patterns continuously repeat by a length of aplurality of times as shown in the following example.SP, SP, SP, SP, A₁, A₁, A₂, A₂, . . . , A_(k), A_(k), SP, SP,  (118)

For determining the head position in the repetition, since a start pointof one period is already obvious based on the amount ofdesynchronization 3814, it can be easily determined by trying to detectthe synchronization sequence or corresponding embedding sequence foreach section that is cut apart as one period length.

<Characteristics of Eighth Embodiment>

According to the digital watermark embedding apparatus and the digitalwatermark detection apparatus of the present embodiment, by embeddingpartial embedding information that is different for each section of thesignal in a time division manner, much amount of embedding informationcan be embedded into the signal.

In digital watermark detection, since synchronization for a start pointof one period can be performed easily, synchronization can be performedefficiently and at high speed so as to detect digital watermark withoutusing a round robin method for trying each shift amount successively,that is, for example, in the case of video signal, a method forsearching for the synchronization signal by performing matching everyone frame shift.

In addition, as a modified example of the digital watermark embeddingapparatus of the present embodiment, the synchronization sequence may beembedded such that the synchronization sequence is superimposed on eachembedding sequence. That is, the embedding pattern generated from thesynchronization sequence is added to the embedding pattern generatedfrom each embedding sequence so as to perform embedding as follows.

SP+A₁, SP+A₂, SP+A₃, . . . , SP+A_(k), SP+A₁, . . .

When embedding is performed like this, in step 2101 when detecting thesynchronization sequence, the synchronization sequence can be detectedaccurately using a sufficient amount of the embedded signal fordetecting the synchronization sequence without dividing the embeddedsignal 923 into a length the same as the period of the periodic signal.Like examples already explained, each embedding sequence can be detectedby dividing the embedded signal based on the amount of desynchronizationobtained from the synchronization sequence.

[Ninth Embodiment]

<Orthogonal Transform Region Embedding>

In the following, a digital watermark embedding apparatus in the ninthembodiment is described.

The present embodiment shows another configuration example of thedigital watermark embedding apparatus in the first embodiment.

<Digital Watermark Embedding Apparatus>

FIG. 68 shows a configuration example of the digital watermark embeddingapparatus and the digital watermark detection apparatus in the ninthembodiment of the present invention.

The digital watermark embedding apparatus 800 in the present embodimentincludes a complex pattern generation unit 810, an embedding patternsuperimposing unit 820, a before-embedding signal transform unit 830, anembedded signal inverse transform unit 840, and a first storage unit850, and the digital watermark embedding apparatus 800 receives theembedding information 911 and the before-embedding signal 912 andoutputs the embedded signal 923.

In the following, operation of the digital watermark embedding apparatus800 is described.

Digital watermark embedding processes by the digital watermark embeddingapparatus 800 are performed by the following procedure.

FIG. 69 is a flowchart of operation of the digital watermark embeddingapparatus in the ninth embodiment of the present invention.

Step 2301) The complex pattern generation unit 810 generates anembedding complex pattern 4021 based on the received embeddinginformation 911 to store it in the first storage unit 850.

Processes of the complex pattern generation unit 810 are the same asthose of the complex pattern generation unit 110 in the digitalwatermark embedding apparatus of the first embodiment.

Step 2302) A signal of a length of a predetermined section T is receivedfrom the before-embedding signal 912.

Step 2303) The before-embedding signal transform unit 830 performs onedimensional discrete Fourier transform for each position (x₁,x₂, . . . ,x_(N−1)) of the section obtained in step 2302 to perform frequencydecomposition to obtain a transformed before embedding signal 4022.

Details of operation of the before-embedding signal transform unit 830are described later.

Step 2304) The embedding pattern superimposing unit 820 superimposes theembedding complex pattern 4021 obtained in step 2301 on the transformedbefore-embedding signal 4022 obtained in step 2303 to obtain beforeinverse transform embedded signal 4023.

Details of operation of the embedding pattern superimposing unit 820 aredescribed later.

Step 2305) The embedded signal inverse transform unit 840 performs onedimensional discrete inverse Fourier transform for each position (x₁,x₂, . . . , x_(N−1)) for the before inverse transform embedded signal4023 obtained in step 2304.

Details of operation of the embedded signal inverse transform unit 840are described later.

Step 2306) Steps 2303-2305 are repeated until the before-embeddingsignal 912 is all processed.

<Digital Watermark Embedding Apparatus—Before—Embedding Signal TransformUnit>

In the following, details of operation of the before-embedding signaltransform unit 830 are described.

The before embedding signal transform unit 830 performs one dimensionaldiscrete Fourier transform on the signal of the section T extracted fromthe before embedding signal 912 to perform frequency decomposition.

In the following, it is described more particularly using equations.

Assuming that the before-embedding signal 912 is I(x₁, x₂, . . . ,x_(N−1), t)

I(x₁, x₂, . . . , x_(N−1), t) is one-dimensional discrete Fouriertransformed as follows to obtain η(x₁, x₂, . . . , x_(N−1), u),

$\begin{matrix}{{\eta\left( {x_{1},x_{2},\cdots\mspace{14mu},x_{N - 1},u} \right)} = {\frac{1}{\sqrt{T}}{\sum\limits_{t = 0}^{T - 1}{{I\left( {x_{1},x_{2},\cdots\mspace{14mu},x_{N - 1},t} \right)}{\mathbb{e}}^{{- j}\;\frac{2\;\pi}{T}{ut}}}}}} & (119)\end{matrix}$wherein T is a predetermined number of samples.

The η(x₁, x₂, . . . , x_(N−1), u) is output as the transformed beforeembedding signal 4022.

<Digital Watermark Embedding Apparatus—Embedding Pattern SuperimposingUnit>

In the following, details of operation of the embedding patternsuperimposing unit 820 are described.

The embedding pattern superimposing unit 820 adds N−1-dimensionalembedding complex pattern 4021 generated by the complex patterngeneration unit 810 to a N−1 dimensional plane part, corresponding to aspecific frequency, of the N-dimensional transformed before embeddingsignal 4022 obtained by the before-embedding signal transform unit 830so that they are superimposed, and the embedding pattern superimposingunit 820 outputs, as the before inverse transform embedded signal 4023,the whole N-dimensional signal including the frequency of the result ofsuperimposing.

It is described concretely in the following using an equation.

Assuming that the transformed before embedding signal 4022 obtained bythe before embedding signal transform unit 830 is η(x₁, x₂, . . . ,x_(N−1), u), and that the embedding complex pattern 4021 obtained by thecomplex pattern generation unit 810 is P(x₁, x₂, . . . , x_(N−1)), andthat the before inverse transform embedded signal 4023 is η′(x₁, x₂, . .. , x_(N−1), u).

$\begin{matrix}{{\eta^{\prime}\left( {x_{1},x_{2},\cdots\mspace{14mu},x_{N - 1},u} \right)} = \left\{ \begin{matrix}{{\eta\left( {x_{1},x_{2},\cdots\mspace{14mu},x_{N - 1},u} \right)} +} & \left( {{{When}\mspace{14mu} u} = u_{0}} \right) \\{{aP}\left( {x_{1},x_{2},\cdots\mspace{14mu},x_{N - 1}} \right)} & \; \\{{\eta\left( {x_{1},x_{2},\cdots\mspace{14mu},x_{N - 1},u} \right)} +} & \left( {{{When}\mspace{14mu} u} = {U - u_{0}}} \right) \\{{aP}^{*}\left( {x_{1},x_{2},\cdots\mspace{14mu},x_{N - 1}} \right)} & \; \\{\eta\left( {x,x,\cdots\mspace{14mu},x,u} \right)} & \left( {{{When}\mspace{14mu} u} \neq u_{0}} \right)\end{matrix} \right.} & (120)\end{matrix}$

In the equation, * represents complex conjugate, u₀ is a predeterminedfrequency, and U is a number of frequency samples. That is, here, u=u₀and u=U−u₀ are selected as the N−1 dimensional plane corresponding tothe frequency u₀. By the way, the reason for providing conjugate complexnumber of P by u=u₀ and u=U−u₀ is that the signal obtained as a resultof discrete inverse Fourier transform becomes a real value.

In addition, similarly to the case of the embedding patternsuperimposing unit 140 of the first embodiment, α is a strengthparameter, and may be configured to be changed according to acharacteristics amount calculated from the whole or a part of thebefore-embedding signal 912.

In addition, also similarly to the case of the embedding patternsuperimposing unit 140 of the first embodiment, when the size of thebefore embedding signal 912 is greater than that of the embeddingcomplex pattern 4021, the embedding complex pattern 4021 may be addedsuch that the embedding complex pattern 4021 is repeated.

In addition, also similarly to the case of the embedding patternsuperimposing unit 140 of the first embodiment, before superimposing theembedding complex pattern, the embedding complex pattern 4021 may beenlarged by a plurality of times or may be enlarged such that the sizematches the size of the before embedding signal 912.

In addition, before superimposing the embedding complex pattern, a partof the transformed embedding signal 4022 that becomes u=u₀ and u=u−u₀for which superimposing is actually performed may be transformed byN−1-dimensional discrete Fourier transform and after that superimposingmay be performed, further, it may be inverse transformed by N−1dimensional discrete inverse Fourier transform.

When performing N−1-dimensional discrete Fourier transform, the processmay be performed as one time N-dimensional discrete Fourier transformtogether with the one dimensional discrete Fourier transform in thebefore embedding signal transform unit 830. In addition, in the sameway, the N−1-dimensional discrete inverse Fourier transform may beperformed as one time N-dimensional discrete inverse Fourier transformtogether with one-dimensional discrete inverse Fourier transform in theafter-mentioned embedded signal inverse transform unit 840. However, byperforming the one-dimensional discrete Fourier transform and theN−1-dimensional discrete Fourier transform separately, and performingthe one-dimensional discrete Fourier inverse transform and theN−1-dimensional discrete Fourier inverse transform separately, there isan advantage that processes can be performed at high speed since it isonly necessary to perform the N−1-dimensional discrete Fourier transformand discrete inverse Fourier transform only on the N−1-dimensional planeof u=u₀ and u=U−u₀ for which superimposing is performed actually.

<Embedded Signal Inverse Transform Unit>

In the following, details of operation of the embedded signal inversetransform unit 840 are described.

The embedded signal inverse transform unit 840 performs one-dimensionalinverse Fourier transform on the before inverse transform embeddedsignal 4023 for each position (x₁, x₂, . . . , x_(N−1)) to obtain theembedded signal 923.

It is described concretely using an equation in the following.

Assuming that the before inverse transform embedded signal 4023 isη′(x₁, x₂, . . . , x_(N−1), u).

By performing one-dimensional discrete inverse Fourier transform onη′(x₁, x₂, . . . , x_(N−1), u) as follows to obtain I′(x₁, x₂, . . . ,x_(N−1), t).

$\begin{matrix}{{I^{\prime}\left( {x_{1},x,\cdots\mspace{14mu},x_{N - 1},t} \right)} = {\frac{1}{\sqrt{U}}{\sum\limits_{u = 0}^{U - 1}{{\eta^{\prime}\left( {x_{1},x_{2},\cdots\mspace{14mu},x_{N - 1},u} \right)}{\mathbb{e}}^{j\;\frac{2\;\pi}{U}{ut}}}}}} & (121)\end{matrix}$

<Characteristics of Ninth Embodiment>

According to the digital watermark embedding apparatus of the presentembodiment, digital watermark that has characteristic similar to that ofthe digital watermark embedding apparatus of the first embodiment can beembedded.

In addition, in the same way as the seventh embodiment, the complexpattern generation unit 810 may generate a plurality of complexpatterns, and the embedding pattern superimposing unit 820 may add eachcomplex pattern to parts of N−1 dimensional plane corresponding to aplurality of frequencies of the transformed before embedding signal4022, so that digital watermark having characteristics similar to thoseof the digital watermark embedding apparatus of the seventh embodimentcan be embedded.

[Other Embodiments]

In the following, as other embodiments of the present invention, aconfiguration example with which each embodiment can be combined isshown.

<Using Pre-Filter when Performing Detection>

In each of first to eighth embodiments, when using the sine wave as theperiodic signal, digital watermark is embedded in a single frequency inthe N-th dimension direction (time direction in the case of videosignal, for example). Also when using other periodic signals, the basicfrequency is most important. Before performing detection by the digitalwatermark detection apparatus, filter processing may be performed forenhancing the corresponding frequency for the embedded signal so as tobe able to detect digital watermark more accurately.

As an example of the filter, a bandpass type filter for enhancingspecific frequency band may be configured using digital filter such asFIR filter and IIR filter. In addition, by using a clipping filter forsuppressing a signal value that exceeds or does not exceed apredetermined threshold to the threshold, or by using non-linear filtersuch as c filter and the like that regards the signal value exceeding apredetermined threshold or being less than the threshold as 0, filterprocessing may be performed such that digital watermark componentremains while efficiently removing noise component for digital watermarksuch as original image component and the like.

In addition, in the seventh embodiment of the present invention,although digital watermark is embedded by using a plurality of frequencybands using a plurality of periodic signals, filter processing may beperformed using respective filter having characteristics for eachperiodic signal before performing temporal demodulation processing foreach periodic signal.

Especially, in the present embodiment, since digital watermark embeddingis performed using a single frequency in the N-th dimension direction,there is no effect to detection performance even by using a filter ofbad phase characteristics with no linear phase characteristics.Therefore, it becomes possible to use a filter, like the IIR filter,that has sharp frequency characteristics with small number of TAPs andthat can perform processing at high speed even though phasecharacteristics is bad, so that accurate digital watermark detectionprocess can be performed at high speed.

<Processes for Embedded Signal>

In each embodiment of the present invention, in FIGS. 10, 52 and 68, forexample, although they are shown such that the embedded signal outputfrom the digital watermark embedding apparatus is directly supplied tothe digital watermark detection apparatus, it is needless to say thatthe embedded signal may be supplied to the digital watermark detectionapparatus after compressing, coding, distributing, editing, modifying,and the are performed on the embedded signal. In addition, it isneedless to say that the embedded signal may be once recorded in amagnetic medium (VTR, DVD, floppy disk, CD, HDD and the like) and othermedium (film and the line), the embedded signal may be transmittedthrough a network, and the embedded signal may be re-taken using takingmeans such as a video camera, a camera of a cellular phone, and a camerausing a film and the like wherein this embedded signal is one reproducedusing an optical device (projecting on a screen as a movie, displayingusing a CRT, or liquid crystal or plasma display, and the like).

<Temporal Modulation Process>

In each embodiment of the present invention, although “temporalmodulation unit” and “temporal demodulation unit” are called like theseas a matter of convenience, it is not necessary to perform modulation inthe time axis direction, and it may be modulation in a differentdimension direction as long as the dimension is orthogonal to N−1dimension.

For example, it is needless to say that, when embedding digitalwatermark into an image signal configured by a two-dimensional signal,one dimensional complex array defined in a lateral direction of theimage may be configured as the N−1 dimensional embedding complexpattern, so that two-dimensional embedding pattern may be obtained bymodulating the embedding complex pattern in a vertical direction. It isneedless to say that vertical and lateral may be switched.

In addition, for example, when embedding digital watermark into threedimensional video signal that is a sum of two dimensions of spacedirection (X, Y) and one dimension of time direction, two-dimensionalcomplex array defined by a lateral direction of image and a timedirection may be configured as the N−1-dimensional embedding complexpattern, so that three-dimensional embedding pattern may be obtained bymodulating the N−1-dimensional embedding complex pattern in the verticaldirection. It is needless to say that vertical and lateral may beswitched.

In addition, in each embodiment of the present invention, an example isdescribed in which the before-embedding signal that is an input signalis a N-dimensional signal, an example may be configured such thatN-dimensional embedding is repeated for M (>N) dimensional input signal.

For example, as to input of a three dimensional video signal that is asum of two dimension of space direction (X, Y) and one dimension of timedirection, each frame image of the video may be regarded as a twodimensional signal, so that embedding may be performed by configuringtwo dimensional embedding pattern by modulating one dimensional complexarray of the lateral direction in the vertical direction, and, byrepeating this for all frames, digital watermark embedding may beperformed. When detecting digital watermark, processes may be performedfor each frame, or processes may be performed for a signal on which eachframe image is superimposed.

<Use of Error Correction Coding and the Like>

In each embodiment of the present invention, before performing processesfor embedding information in the embedding sequence generation unit, theembedding information may be coded using error correction code, andinversely, before outputting detection information, the error correctioncode may be decoded.

<N−1-Dimensional Orthogonal Transform>

Although the Third Embodiment of the present invention is describedusing discrete Fourier transform as an example of orthogonal transformfor the N−1-dimensional complex pattern in the N−1-dimensional inverseFourier transform unit 113 and the N−1-dimensional Fourier transformunit 225, an orthogonal transform method, other than the discreteFourier transform, for performing transform from complex numbers tocomplex numbers may be used.

By the way, for correctly processing desynchronization in N-th dimensiondirection in an orthogonal transformed region, it is only necessary thatthe coefficient e^(jΔθ) that occurs due to desynchronization in N-thdimension direction is preserved in the transform. Since orthogonaltransform is linear transform, the condition is already satisfied as thetransform is orthogonal transform.

<One Dimensional Linear Transform>

In addition, in the second embodiment, although discrete Fouriertransform is used as one dimensional transform in the temporalmodulation unit 130 b, any linear transform method, other than discreteFourier transform, that performs transform from complex numbers tocomplex numbers may be used as long as the linear transform method has aperiodic function, as a base, satisfying the following conditions andhas an inverse transform.

In addition, in the same way, in the ninth embodiment of the presentinvention, although one-dimensional discrete Fourier transform andone-dimensional discrete inverse Fourier transform are used as anexample of one dimensional transform in the before embedding signaltransform unit 830 and the embedded signal inverse transform unit 840,any linear transform method, other than discrete Fourier transform, thatperforms transform from complex numbers to complex numbers may be usedas long as the linear transform method has a periodic function, as abase, satisfying the following conditions and has an inverse transform.

Conditions:

1) A result obtained by performing integration for one period becomes 0.

2) Autocorrelation function does not have sharp peak.

Details of these conditions are already described as an example ofperiodic signal.

For example, a following linear transform may be used.

Considering linear transform offrom vector {right arrow over (x)}ε{right arrow over (c)} ^(n) to vector{right arrow over (y)}ε{right arrow over (C)} ^(n)

and assuming that transform matrix indicating the transform is A,wherein C indicates a set of the whole of the complex numbers. Inaddition,{right arrow over (y)}=A{right arrow over (x)}  (122)in which{right arrow over (x)}=(x₁x₂ . . . x_(n))  (123){right arrow over (y)}=(y₁y₂ . . . y_(n))  (124)

$\begin{matrix}{A = \begin{pmatrix}a_{0,0} & a_{0,1} & \cdots & a_{0,{n - 1}} \\\vdots & \; & \; & \; \\a_{i,0} & a_{i,1} & \cdots & a_{i,{n - 1}} \\\vdots & \; & \; & \; \\a_{{n - 1},0} & a_{{n - 1},1} & \cdots & a_{{n - 1},{n - 1}}\end{pmatrix}} & (125)\end{matrix}$

Assuming that f(t) is a periodic function having a period n thatsatisfies the above conditions, linear transform represented by thetransform matrix A may be used wherein

$\begin{matrix}{a_{ik} = {{f\left( {{\mathbb{i}}\; k} \right)} + {j\;{f\left( {{{\mathbb{i}}\; k} - \frac{n}{4\; i}} \right)}}}} & (126)\end{matrix}$in which j is the imaginary unit.

The f(t) may be (FIG. 4A) (a) sine wave, (FIG. 4B)(b) triangular wave,or (FIG. 4C) (C) rectangular wave shown in FIG. 4A-C.

<Use as Synchronization Signal>

In the fifth embodiment of the present invention, although a method isdescribed for detecting the amount of desynchronization in the timedirection using the embedding pattern itself representing embeddinginformation, the method for detecting the amount of desynchronization ofthe present invention may be combined and used with arbitrary digitalwatermark methods. That is, a digital watermark embedding apparatus maybe configured so as to embed a specific synchronization signal using thedigital watermark embedding method of the present invention togetherwith digital watermark embedding by using arbitrary digital watermarkingmethod, and, then, a digital watermark detection apparatus may beconfigured so as to perform synchronization from the synchronizationsignal using the detection method of the amount of desynchronization ofthe present invention, and after that, to detect and output embeddinginformation using arbitrary digital watermark detection method.

In addition, the period of the periodic signal for embedding thesynchronization sequence may be configured to be an integral multiple ofthe period of the periodic signal for embedding the embedding sequence.

<Others>

Configurations shown in each embodiment of the present invention may beused by combining them as necessary.

In addition, operation of each configuration element of the digitalwatermark embedding apparatus and the digital watermark detectionapparatus in each embodiment may be constructed as a program, and theprogram may be installed in a computer to execute it or the program canbe distributed via a network.

In addition, the constructed program may be stored in a movable storagemedium such as a hard disk, a flexible disk, CD-ROM and the like, sothat the program may be installed in a computer, or may be distributed.

As described above, according to an embodiment of the present invention,a digital watermark embedding apparatus for embedding embeddinginformation, as digital watermark, into an input signal havingdimensions equal to or greater than N (N is an integer equal to orgreater than 2) such that it is imperceptible to human senses,including: embedding sequence generation means configured to generate anembedding sequence based on the embedding information to store it infirst storage means; array generation means configured to generate aN−1-dimensional pattern based on the embedding sequence in the firststorage means; modulation means configured to modulate a periodic signalaccording to a value on the N−1-dimensional pattern to generate aN-dimensional embedding pattern and store it in second storage means;and embedding pattern superimposing means configured to obtain theN-dimensional embedding pattern stored in the second storage means tosuperimpose the embedding pattern on the input signal so as to embed it,is provided.

According to this digital watermark embedding apparatus, by modulatingthe N−1-dimensional pattern in the N-th dimension direction andembedding it, because of redundancy obtained by spreading embeddinginformation of the N−1-dimensional pattern into the N-dimensional space,information having long information length can be embedded as digitalwatermark in which there is sufficient tolerance for modification suchas high compression and re-taking, for example, and qualitydeterioration can be suppressed.

In addition, by using the embedding sequence that is spectrum spread inthe N−1-dimensional space, digital watermark that does not requiresynchronization or that makes it possible to perform synchronizationeasily and rapidly can be embedded irrespective of the amount ofdesynchronization in the N-th dimension direction.

The modulation means may be configured to generate the N-dimensionalembedding pattern such that phases in a direction of a N-th dimensionare different with each other according to a position on theN−1-dimensional pattern. According to this configuration, by embeddingdigital watermark by using the phase of the periodic signal, modulationcan be performed for the N−1-dimensional pattern easily and at highspeed in the N-th dimension direction. In addition to that, by usingphase shift of the periodic signal, digital watermark that does notrequire synchronization or that makes it possible to performsynchronization easily and at high speed can be embedded irrespective ofthe amount of desynchronization in the N-th dimension direction. Inaddition, it can be prevented to produce a frame in which digitalwatermark becomes less than the minimum video signal quantization valueso that digital watermark embedding is not performed actually, and thevideo signal as a transmission route of digital watermark can be usedeffectively and robustness can be increased for the attack for aimingand changing a frame in which amplitude of digital watermark is large.

In addition, since the phase is spread on the N−1-dimensional space ofthe embedding pattern, the size of the noise component that appears dueto the before-embedding signal in the result of the correlationcalculation becomes smaller, and as a result, digital watermarkembedding and detection becomes possible with higher reliability, anddigital watermark embedding and detection becomes possible withreliability similar to conventional one and with less qualitydeterioration.

In addition, by embedding digital watermark by using the sum of twoperiodic signals that have same basic frequency and that are orthogonal,modulation can be performed for the N−1-dimensional pattern easily andat high speed in the N-th dimension direction. In addition to that, byusing phase shift of the periodic signal, digital watermark that doesnot require synchronization or that makes it possible to performsynchronization easily and at high speed can be embedded irrespective ofthe amount of desynchronization in the N-th dimension direction.

In addition, by using a periodic function, such as a rectangular waveand a triangular wave as a periodic signal, that has characteristic inwhich autocorrelation function does not have sharp peak, and by whichcalculation can be easily performed compared with a sine wave, digitalwatermark embedding process can be realized at higher speed even in anenvironment in which computational resources are limited.

In addition, by using linear transform such as discrete Fouriertransform for modulation, modulation can be performed for theN−1-dimensional pattern easily and at high speed in the N-th dimensiondirection by using fast Fourier transform, for example. In addition tothat, by using linear transform coefficient such as discrete Fouriertransform coefficient, digital watermark that does not requiresynchronization or that makes it possible to perform synchronizationeasily and at high speed can be embedded irrespective ofdesynchronization in the N-th dimension direction.

In the digital watermark embedding apparatus, the N−1-dimensionalpattern is a complex number pattern, and the array generation means maygenerate the N−1-dimensional pattern such that a part of the embeddingsequence becomes the real part and a part of the embedding sequencebecomes the imaginary part.

According to this configuration, embedding is performed using the realpart and the imaginary part of the complex number, there is norestriction on symmetry property of the pattern, embedding can beperformed using the whole N−1-dimensional space, the length of spectrumspread sequence can be made longer, reliability for detection is high,and information having longer embedding information length can beembedded as digital watermark with reliability similar to conventionalone, and digital watermark with less quality deterioration can beembedded with reliability and information length similar to conventionalone.

In the digital watermark embedding, the N−1-dimensional pattern is acomplex number pattern, and the modulation means may modulate theperiodic signal such that an argument of a complex number on theN−1-dimensional pattern becomes a phase of the modulation signal, and anabsolute value of the complex number becomes the size of the modulationsignal.

According to this configuration, digital watermark that does not requiresynchronization or that makes it possible to perform synchronizationeasily and rapidly can be embedded irrespective of the amount ofdesynchronization in the N-th dimension direction. In addition, sincethe argument of the complex number becomes the phase of the modulationsignal in a direction of the axis of the N-th dimension, it can beprevented to produce a frame in which digital watermark becomes lessthan the minimum video signal quantization value so that digitalwatermark embedding is not performed actually, and the video signal as atransmission route of digital watermark can be used effectively androbustness can be increased for the attack for aiming and changing aframe in which amplitude of digital watermark is large.

In addition, the digital watermark embedding apparatus may be configuredsuch that, the embedding sequence generation means divides the generatedembedding sequence to generate a plurality of embedding sequences tostore them in the first storage means; the array generation meansgenerates N−1-dimensional patterns corresponding to each of theplurality of embedding sequences stored in the first storage; themodulation means generates N-dimensional embedding patterns eachcorresponding to the N−1-dimensional pattern to store the N-dimensionalembedding patterns in the second storage means; and the embeddingpattern superimposing means adds all of the embedding patterns stored inthe second storage means, and after that, superimposes it on the inputsignal.

According to this configuration, by embedding information using aplurality of periodic signals, embedding information of longerinformation length can be embedded as digital watermark, and reliabilityof detection result can be made clear more accurately, and in additionto that, the length of spectrum spread sequence can be made longer, sothat digital watermark embedding with higher reliability can beperformed.

In addition, according to an embodiment of the present invention, adigital watermark embedding apparatus for embedding embeddinginformation, as digital watermark, into an input signal havingdimensions equal to or greater than N(N is an integer equal to orgreater than 2) such that it is imperceptible to human senses,including: embedding sequence generation means configured to generate anembedding sequence based on the embedding information to store it infirst storage means; array generation means configured to generate aN−1-dimensional pattern based on the embedding sequence stored in thefirst storage means; transform means configured to orthogonal transformthe input signal to obtain a transformed signal; embedding patternsuperimposing means configured to superimpose the N−1-dimensionalpattern stored in the second storage means on a N−1 dimensional planethat is a part of the transformed signal to obtain a before-inversetransform signal; and inverse transform means configured to orthogonalinverse transform the before inverse transform signal to obtain anembedded signal, is provided.

According to this digital watermark embedding apparatus, by performingembedding by superimposing the N−1-dimensional pattern on thebefore-embedding signal as a signal in the N-th dimension direction,because of redundancy obtained by spreading embedding information of theN−1-dimensional pattern into the N-dimensional space, information havinglong information length can be embedded as digital watermark in whichthere is sufficient tolerance for modification such as high compressionand re-taking, for example, and quality deterioration can be suppressed.In addition, there is no restriction on symmetry property of thepattern, embedding can be performed using the whole N−1-dimensionalspace, the length of spectrum spread sequence can be made longer,reliability for detection is high, and information having longerembedding information length can be embedded as digital watermark withreliability similar to conventional one, and digital watermark with lessquality deterioration can be embedded with reliability and informationlength similar to conventional one. In addition, by using the embeddingsequence that is spectrum spread in the N−1-dimensional space, digitalwatermark that does not require synchronization or that makes itpossible to perform synchronization easily and rapidly can be embeddedirrespective of the amount of desynchronization in the N-th dimensiondirection. In addition, it can be prevented to produce a frame in whichdigital watermark becomes less than the minimum video signalquantization value so that digital watermark embedding is not performedactually, and the video signal as a transmission route of digitalwatermark can be used effectively and robustness can be increased forthe attack for aiming and changing a frame in which amplitude of digitalwatermark is large.

The digital watermark embedding apparatus may be configured such that,the embedding sequence generation means generates a plurality ofembedding sequences to store them in the first storage means; the arraygeneration means generates N−1-dimensional patterns each correspondingto one of the plurality of embedding sequences stored in the firststorage means to store them in the second storage means; and theembedding pattern superimposing means superimposes the N−1-dimensionalpatterns stored in the second storage means on a plurality ofN−1-dimensional planes of the transformed signal respectively.

According to this configuration, by superimposing the N−1-dimensionalpattern on the plurality of N−1-dimensional plane of the transformedsignal, embedding information of longer information length can beembedded as digital watermark, and reliability of detection result canbe made clear more accurately, and in addition to that, the length ofspectrum spread sequence can be made longer, so that digital watermarkembedding with higher reliability can be performed.

In addition, according to an embodiment of the present invention, adigital watermark detection apparatus for detecting digital watermarkthat is embedded beforehand into an input signal having dimensions equalto or greater than N(N is an integer equal to or greater than 2) suchthat it is imperceptible to human senses, including: demodulation meansconfigured to measure a component of a predetermined periodic signal ina direction of a dimension in the input signal to obtain aN−1-dimensional pattern; detection sequence extraction means configuredto obtain a detection sequence from values of the N−1-dimensionalpattern to store the detection sequence in storage means; andcorrelation value calculation means configured to detect the embeddeddigital watermark based on a size of a correlation value between thedetection sequence stored in the storage means and an embeddingsequence, is provided.

According to this digital watermark detection apparatus, because ofredundancy obtained by spreading embedding information of theN−1-dimensional pattern into the N-dimensional space, information havinglong information length can be detected as digital watermark in whichthere is sufficient tolerance for modification such as high compressionand re-taking, for example, and quality deterioration can be suppressed.In addition, by using the embedding sequence that is spectrum spread inthe N−1-dimensional space, digital watermark that does not requiresynchronization or that makes it possible to perform synchronizationeasily and rapidly can be detected irrespective of the amount ofdesynchronization in the N-th dimension direction.

In addition, by using linear transform such as discrete Fouriertransform for demodulation, the N−1-dimensional pattern can bedemodulated easily and at high speed from the N-dimensional signal byusing fast Fourier transform and the like, for example. In addition tothat, by using linear transform coefficient such as discrete Fouriertransform coefficient, digital watermark that does not requiresynchronization or that makes it possible to perform synchronizationeasily and at high speed can be detected irrespective ofdesynchronization in the N-th dimension direction.

The demodulation means may be configured to generate two periodicsignals that have a same frequency and that are orthogonal with eachother to obtain the N−1-dimensional pattern based on correlation betweenthe input signal and the periodic signals.

According to this configuration, the N−1-dimensional pattern can bedemodulated easily and at high speed in the N-th dimension direction. Inaddition to that, by using phase shift of the periodic signal, digitalwatermark detection that does not require synchronization or that makesit possible to perform synchronization easily and at high speed can beperformed irrespective of the amount of desynchronization in the N-thdimension direction.

In addition, by using a periodic function, such as a rectangular waveand a triangular wave as a periodic signal, that has characteristic inwhich autocorrelation function does not have sharp peak, and by whichcalculation can be easily performed compared with a sine wave, digitalwatermark detection process can be realized at higher speed even in anenvironment in which computational resources are limited.

In addition, the demodulation means may be configured to demodulate theinput signal based on a difference or differentiation value in adirection of N-th dimension.

According to this configuration, by performing demodulation by theperiodic signal using difference or differentiation of the signal,digital watermark detection with high detection accuracy becomespossible, and a digital watermark scheme with smaller signaldeterioration becomes possible with detection performance of similarextent.

In the digital watermark detection apparatus, the N−1-dimensionalpattern is a complex number pattern, and the detection sequenceextraction means may obtain the detection sequence based on values ofthe real part and the imaginary part of the N−1-dimensional pattern tostore them in the storage means.

According to this configuration, because of detection of digitalwatermark embedded using the real part and the imaginary part of thecomplex number, there is no restriction on symmetry property of thepattern, and embedding is performed using the whole N−1-dimensionalspace, thus, the length of spectrum spread sequence can be made longer,reliability for detection is high, and longer embedding information canbe detected as digital watermark with reliability similar toconventional one, and digital watermark detection with less qualitydeterioration can be performed with reliability and information lengthsimilar to conventional one.

In addition, in the digital watermark detection apparatus, theN−1-dimensional pattern is a complex number pattern, and the correlationvalue calculation means may obtain complex correlation values for eachbit, aligns directions of the complex correlation values for each bit,and after that, calculates a total sum of the complex correlation valuesto detect embedded digital watermark based on the total sum. Accordingto this configuration, bit determination error becomes smaller comparedwith detection for each bit, so that higher robustness can be realized.

In addition, in the digital watermark detection apparatus, theN−1-dimensional pattern is a complex number pattern, and the correlationvalue calculation means may detect embedded digital watermark based onthe absolute value of the complex correlation value.

According to this configuration, by performing detection using theabsolute value of the complex correlation value, correlation to theembedding sequence can be obtained even for an input signaldesynchronized in the N-th dimension direction, so that digitalwatermark detection in which synchronization is unnecessary can beperformed.

In addition, in the digital watermark embedding apparatus, theN−1-dimensional pattern is a complex number pattern, and the correlationvalue calculation means may obtain complex correlation values for eachbit, align directions of the complex correlation values for each bit,and after that, calculate a total sum of the complex correlation values,and the digital watermark detection apparatus may includesynchronization means configured to obtain an amount ofdesynchronization of the input signal based on an argument of the totalsum. By this configuration, the amount of desynchronization can bemeasured, so that digital watermark detection by easy and fastsynchronization becomes possible. In addition, by obtaining the amountof desynchronization based on the complex correlation value for eachbit, the amount of desynchronization can be measure with higherreliability and more accurately.

In the digital watermark detection apparatus, the N−1-dimensionalpattern is a complex number pattern, and the digital watermark detectionapparatus may include synchronization means configured to obtain theamount of desynchronization of the input signal based on an argument ofa complex correlation value between the detection sequence and theembedding sequence.

By performing detection using the argument of the complex correlationvalue, correlation to the embedding sequence can be obtained even for aninput signal desynchronized in the N-th dimension direction, so that theamount of desynchronization can be measured, and digital watermarkdetection by easy and fast synchronization becomes possible.

The digital watermark detection apparatus may be configured such thatthe demodulation means measures phases of a plurality of periodicsignals to obtain a plurality of N−1-dimensional patterns; thesynchronization means obtains an amount of desynchronization for each ofthe plurality of N−1-dimensional patterns; the detection sequenceextraction means obtains detection sequences from each of the pluralityof N−1-dimensional patterns by correcting synchronization based oncorresponding one of the amount of desynchronization so as to store thedetection sequences in the storage means; and the correlation valuecalculation means calculates a correlation value between a sequenceobtained by connecting the detection sequences stored in the storagemeans obtained for each of the plurality of N−1-dimensional patterns andthe embedding sequence.

According to this configuration, by detecting digital watermark embeddedusing a plurality of periodic signals, embedding information of longerinformation length can be detected as digital watermark, and reliabilityof detection result can be made clear more accurately, and in additionto that, the length of spectrum spread sequence can be made longer, sothat digital watermark detection with higher reliability can beperformed.

The synchronization means may obtain a whole shift amount in an axisdirection of a N-th dimension based on the amounts of desynchronizationobtained for each of the plurality of N−1-dimensional patterns.According to this configuration, the amount of desynchronization of eachdetection complex pattern can be obtained accurately, so that, digitalwatermark detection with high detection accuracy becomes possible, anddigital watermark detection with smaller signal deterioration becomespossible with detection performance of similar extent.

In addition, the synchronization means may detect a synchronizationsequence that is embedded beforehand, performs synchronization,re-divides the input signal according to the amount ofdesynchronization, and includes detection means configured to detectplurality of remaining pieces of embedding information. According tothis configuration, by detecting embedding information divided in thetime direction, longer embedding information can be embedded in asignal, so that applications applied to digital watermarking can beenlarged.

In addition, according to an embodiment of the present invention, adigital watermark embedding program for embedding embedding information,as digital watermark, into an input signal having dimensions equal to orgreater than N(N is an integer equal to or greater than 2) such that itis imperceptible to human senses, the digital watermark embeddingprogram causing a computer to function as embedding sequence generationmeans configured to generate an embedding sequence based on theembedding information to store it in first storage means; arraygeneration means configured to generate a N−1-dimensional pattern basedon the embedding sequence in the first storage means; modulation meansconfigured to modulate a periodic signal according to a value on theN−1-dimensional pattern to generate a N-dimensional embedding patternand store it in second storage means; and embedding patternsuperimposing means configured to obtain the N-dimensional embeddingpattern stored in the second storage means to superimpose the embeddingpattern on the input signal so as to embed it, is provided.

In addition, according to an embodiment of the present invention, adigital watermark embedding program for embedding embedding information,as digital watermark, into an input signal having dimensions equal to orgreater than N(N is an integer equal to or greater than 2) such that itis imperceptible to human senses, the digital watermark embeddingprogram causing a computer to function as embedding sequence generationmeans configured to generate an embedding sequence based on theembedding information to store it in first storage means; arraygeneration means configured to generate a N−1-dimensional pattern basedon the embedding sequence stored in the first storage means; transformmeans configured to orthogonal transform the input signal to obtain atransformed signal; embedding pattern superimposing means configured tosuperimpose the N−1-dimensional pattern stored in the second storagemeans on a N−1 dimensional plane that is a part of the transformedsignal to obtain a before-inverse transform signal; and inversetransform means configured to orthogonal inverse transform the beforeinverse transform signal to obtain an embedded signal, is provided.

In addition, according to an embodiment of the present invention, adigital watermark detection program for detecting digital watermark thatis embedded beforehand into an input signal having dimensions equal toor greater than N(N is an integer equal to or greater than 2) such thatit is imperceptible to human senses, the digital watermark detectionprogram causing a computer to function as demodulation means configuredto measure a component of a predetermined periodic signal in a directionof a dimension in the input signal to obtain a N−1-dimensional pattern;detection sequence extraction means configured to obtain a detectionsequence from values of the N−1-dimensional pattern to store thedetection sequence in storage means; and correlation value calculationmeans configured to detect the embedded digital watermark based on asize of a correlation value between the detection sequence stored in thestorage means and an embedding sequence.

INDUSTRIAL APPLICABILITY

The present invention can be applied to a technique for embeddingdigital watermark into a still image and a moving image, and applied toa technique for detecting the digital watermark.

By the way, the present invention is not limited to the specificallydisclosed embodiments, and variations and modifications may be madewithout departing from the scope of the present invention.

The present international application claims priority based on Japanesepatent application No. 2006-061745, filed in the JPO on Mar. 7, 2006,and the entire contents of the application are incorporated herein byreference.

The invention claimed is:
 1. A digital watermark detecting method for detecting a digital watermark that is embedded beforehand into an input signal having dimensions equal to or greater than N (N is an integer equal to or greater than 2) such that it is imperceptible to human senses in a digital watermark detection apparatus including demodulation means, detection sequence extraction means, correlation value calculation means, and storage means, the method comprising: measuring, at the demodulation means, a component of a predetermined periodic signal in a direction of a dimension in the input signal to obtain a N−1-dimensional pattern; obtaining, at the detection sequence extraction means, a detection sequence from values of the N−1-dimensional pattern and storing the detection sequence in the storage means; and detecting, at the correlation value calculation means, the embedded digital watermark based on a size of a correlation value between the detection sequence stored in the storage means and an embedding sequence.
 2. The digital watermark detection method as claimed in claim 1, wherein the demodulation means generates two periodic signals that have a same frequency and that are orthogonal with each other to obtain the N−1-dimensional pattern based on correlation between the input signal and the periodic signals.
 3. The digital watermark detection method as claimed in claim 1 or 2, wherein the demodulation means demodulates the input signal based on a difference or differentiation value in a direction of N-th dimension.
 4. The digital watermark detection method as claimed in claim 1 or 2, wherein the N−1-dimensional pattern is a complex number pattern or a pattern of a two-dimensional vector, and the detection sequence extraction means obtains the detection sequence based on values of the real part and the imaginary part of the N−1-dimensional pattern to store them in the storage means.
 5. The digital watermark detection method as claimed in claim 1 or 2, wherein the N−1-dimensional pattern is a complex number pattern, and the correlation value calculation means obtains complex correlation values for each bit, aligns directions of the complex correlation values for each bit, and after that, calculates a total sum of the complex correlation values to detect embedded digital watermark based on the total sum.
 6. The digital watermark detection method as claimed in claim 1 or 2, wherein the N−1-dimensional pattern is a complex number pattern, and the correlation value calculation means detects embedded digital watermark based on the absolute value of the complex correlation value.
 7. The digital watermark detection method as claimed in claim 1 or 2, wherein the N−1-dimensional pattern is a complex number pattern, and the correlation value calculation means obtains complex correlation values for each bit, aligns directions of the complex correlation values for each bit, and after that, calculates a total sum of the complex correlation values, and the synchronization means obtains an amount of desynchronization of the input signal based on an argument of the total sum.
 8. The digital watermark detection method as claimed in claim 1 or 2, wherein the N−1-dimensional pattern is a complex number pattern, and the synchronization means obtains the amount of desynchronization of the input signal based on an argument of a complex correlation value between the detection sequence and the embedding sequence.
 9. The digital watermark detection method as claimed in claim 8, wherein, the synchronization means detects a synchronization sequence that is embedded beforehand, performs synchronization, re-divides the input signal based on the amount of desynchronization to detect plurality of remaining pieces of embedding information.
 10. The digital watermark detection method as claimed in claim 1, wherein the demodulation means measures phases of a plurality of periodic signals to obtain a plurality of N−1-dimensional patterns; the synchronization means obtains an amount of desynchronization for each of the plurality of N−1-dimensional patterns; the detection sequence extraction means obtains the detection sequences by correcting synchronization for each of the plurality of N−1-dimensional patterns based on corresponding one of the amount of desynchronization so as to store the detection sequences in the storage means; and the correlation value calculation means calculates a correlation value between a sequence obtained by connecting the detection sequences stored in the storage means obtained for each of the plurality of N−1-dimensional patterns and the embedding sequence.
 11. The digital watermark detection method as claimed in claim 10, wherein, the synchronization means obtains a whole shift amount in an axis direction of a N-th dimension based on the amount of desynchronization obtained for each of the plurality of N−1-dimensional patterns.
 12. A digital watermark detection apparatus for detecting a digital watermark that is embedded beforehand into an input signal having dimensions equal to or greater than N (N is an integer equal to or greater than 2) such that it is imperceptible to human senses, comprising: demodulation means configured to measure a component of a predetermined periodic signal in a direction of a dimension in the input signal and obtain a N−1-dimensional pattern; detection sequence extraction means configured to obtain a detection sequence from values of the N−1-dimensional pattern and store the detection sequence in storage means; and correlation value calculation means configured to detect the embedded digital watermark based on a size of a correlation value between the detection sequence stored in the storage means and an embedding sequence.
 13. The digital watermark detection apparatus as claimed in claim 12, wherein the demodulation means generates two periodic signals that have a same frequency and that are orthogonal with each other to obtain the N−1-dimensional pattern based on correlation between the input signal and the periodic signals.
 14. The digital watermark detection apparatus as claimed in claim 12 or 13, wherein the demodulation means demodulates the input signal based on a difference or differentiation value in a direction of N-th dimension.
 15. The digital watermark detection apparatus as claimed in claim 12 or 13, wherein the N−1-dimensional pattern is a complex number pattern or a pattern of a two-dimensional vector, and the detection sequence extraction means obtains the detection sequence based on values of the real part and the imaginary part or elements of the two-dimensional vector of the N−1-dimensional pattern to store them in the storage means.
 16. The digital watermark detection apparatus as claimed in claims 12 to 13, wherein the N−1-dimensional pattern is a complex number pattern, and the correlation value calculation means obtains complex correlation values for each bit, aligns directions of the complex correlation values for each bit, and after that, calculates a total sum of the complex correlation values to detect embedded digital watermark based on the total sum.
 17. The digital watermark detection apparatus as claimed in claim 12 or 13, wherein the N−1-dimensional pattern is a complex number pattern, and the correlation value calculation means detects embedded digital watermark based on the absolute value of the complex correlation value.
 18. The digital watermark detection apparatus as claimed in claim 12, wherein the N−1-dimensional pattern is a complex number pattern, and the correlation value calculation means obtains complex correlation values for each bit, aligns directions of the complex correlation values for each bit, and after that, calculates a total sum of the complex correlation values, and the digital watermark detection apparatus comprising synchronization means configured to obtain an amount of desynchronization of the input signal based on an argument of the total sum.
 19. The digital watermark detection apparatus as claimed in claim 12 or 13, wherein the N−1-dimensional pattern is a complex number pattern, and the digital watermark detection apparatus comprising synchronization means configured to obtain the amount of desynchronization of the input signal based on an argument of a complex correlation value between the detection sequence and the embedding sequence.
 20. The digital watermark detection apparatus as claimed in claim 19, wherein the demodulation means measures phases of a plurality of periodic signals to obtain a plurality of N−1-dimensional patterns; the synchronization means obtains an amount of desynchronization for each of the plurality of N−1-dimensional patterns; the detection sequence extraction means obtains detection sequences from each of the plurality of N−1-dimensional patterns by correcting synchronization based on corresponding one of the amount of desynchronization so as to store the detection sequences in the storage means; and the correlation value calculation means calculates a correlation value between a sequence obtained by connecting the detection sequences stored in the storage means obtained for each of the plurality of N−1-dimensional patterns and the embedding sequence.
 21. The digital watermark detection apparatus as claimed in claim 20, wherein, the synchronization means obtains a whole shift amount in an axis direction of a N-th dimension based on the amounts of desynchronization obtained for each of the plurality of N−1-dimensional patterns.
 22. The digital watermark detection apparatus as claimed in claim 19, wherein, the synchronization means detects a synchronization sequence that is embedded beforehand, performs synchronization, re-divides the input signal according to the amount of desynchronization, and includes detection means configured to detect plurality of remaining pieces of embedding information.
 23. A non-transitory computer readable storage medium storing a digital watermark detection program for detecting digital watermark that is embedded beforehand into an input signal having dimensions equal to or greater than N (N is an integer equal to or greater than 2) such that it is imperceptible to human senses, the digital watermark detection program causing a computer to function as the digital watermark detection apparatus as claimed in claim 12 or
 13. 24. A digital watermark detection apparatus for detecting digital watermark that is embedded beforehand into an input signal having dimensions equal to or greater than N (N is an integer equal to or greater than 2) such that it is imperceptible to human senses, comprising: circuitry configured to: measure a component of a predetermined periodic signal in a direction of a dimension in the input signal and obtain a N−1-dimensional pattern; obtain a detection sequence from values of the N−1-dimensional pattern and store the detection sequence in a storage unit; and detect the embedded digital watermark based on a size of a correlation value between the detection sequence stored in the storage unit and an embedding sequence. 